Lemon Bars
A shortbread base baked until it is genuinely dry, with the lemon filling poured on while both are hot so the two set as a single layer.
- Prep
- 25 min
- Cook
- 55 min
- Resting
- 2 hr
- Total
- 3 hr 20 min
- Serves
- 16
- Revisions
- 1
Allergens
- Cereals containing gluten
- Eggs
- Milk
Named from the ingredients as written, including those carried in from sub-recipes. This is not a guarantee — check the labels on what you actually buy, and note that a product’s recipe can change.
Ingredients
Serves
Base
Lemon filling
To finish
Method
Base
Heat the oven to 170C/340F.
Butter a 20cm square tin and line it with baking paper, leaving an overhang on two sides.
Rub the cold butter into the 200g of flour, the 60g of icing sugar and the 3g of fine salt with your fingertips, until the mixture looks like damp sand.
Tip the crumbs into the tin and press them into an even layer with the flat bottom of a glass, firming them into the corners.
Chill the lined tin for 15 minutes.
Bake for 25-30 minutes, until the base is pale gold across the whole surface and completely dry, with no damp grey patches left in the middle.
Bake the base until it is genuinely done. Filling poured onto an underbaked base soaks straight into it, and the bar comes out with a wet, pasty layer where the biscuit should be.
Lemon filling
Whisk the eggs and the caster sugar together in a bowl until smooth, stirring rather than beating so no air goes in.
Whisk in the 40g of flour until there are no lumps left.
Whisk in the lemon zest, the 150ml of juice and the 1g of fine salt.
Skim any foam off the surface with a spoon. Bubbles bake into a pale mottled crust across the top of the finished bars.
Turn the oven down to 150C/300F.
Pour the filling over the base the moment the base comes out of the oven, while both are hot.
Pouring onto a hot base is what fuses the two together. Onto a cold one the filling sets as a separate sheet and lifts cleanly off the biscuit in one piece as soon as anybody bites it.
Bake for 20-25 minutes, until the filling is set to the edges and only the middle 4cm shivers when you tap the side of the tin.
Take it out while the centre still moves. Baked until firm, the filling has boiled: it sets grainy and weeps a layer of water onto the surface as it cools, and there is no way back from that.
Cool the tin on a rack for 1 hour.
Refrigerate for at least another hour, until cold right through.
To finish
Lift the slab out by the paper onto a board.
Cut into 16 bars with a long knife dipped in hot water and wiped dry between every cut.
Dust with icing sugar just before serving. Dusted while the surface is still cold and damp, the sugar dissolves into a wet film within the hour.
Nobody has rated this recipe yet.
Sign in to rate this recipe. One rating per person, and you can change it.
What to expect
- Taste
Sharp, and it should be sharp before it is sweet — 150ml of lemon juice against 300g of sugar is a deliberately aggressive ratio and it is what stops the bar being sickly. The lemon reads as bright and clean rather than as sourness, with the zest contributing a perfumed, slightly bitter edge that juice alone does not have. Underneath, the base is plain, buttery and barely sweet, and it exists to give the mouth something neutral against all that acid. Salt is present in both layers and is doing quiet work in each. The icing sugar on top is a moment of straightforward sweetness before any of it starts.
- Aroma
Lemon, strongly, and mostly from the zest rather than the juice — the oils in the peel are volatile and the smell of the raw filling is one of the best in the collection. The baked bar smells much less, since a set custard holds its aroma in. The base smells of shortbread while it is baking.
- Texture
The contrast is the recipe. The base is short, sandy and crumbly and gives resistance for a moment. The filling is dense, smooth and slightly wobbly, closer to a set curd than to a cake, and it should be completely free of graininess — grain means it was baked too hot. The icing sugar on top is powdery and momentary. There is nothing crisp anywhere and nothing chewy.
- Sound
The knife going through, which should be a single clean pass with no drag.
- How the flavour moves
Icing sugar first, sweet and immediately gone. Then the acid arrives hard and fills the whole mouth, and it is genuinely startling in a good bar. Butter and biscuit come up underneath it about halfway through and take the edge off. The finish is long and citric with a faint bitterness from the zest, and it leaves the mouth clean and wanting another one — which is the mark of the ratio being right. If the finish is sweet rather than sharp, there was not enough lemon.
- Serve it
Cold or cool, and this is one of the few sweet things here that is better from the fridge. Cold sharpens the acidity and firms the filling; at room temperature it softens and reads sweeter and flabbier.
- Goes with
Tea, coffee, or as a dessert with a spoonful of cream. Very good after something rich, because the acidity does the job a sorbet would.
Cook's notes
- Difficulty
Easy, with two moments of judgement: how far to bake the base, and when to stop baking the filling.
- Cost
Low. Four lemons is the only cost of any size.
- Equipment
A 20cm square tin, baking paper, a bowl and a whisk. A fine grater for the zest.
- When to make it
Any time. It needs three hours including cooling, so it is an afternoon-for-evening recipe.
- Best season
Lemons are at their best in winter, which makes this a better January recipe than most people assume.
- You know it is done when
The base is done when it is pale gold over the whole surface with no damp grey patches in the middle. The filling is done when it has lost its liquid shine and is set right up to the edges, with only the middle 4cm shivering when the tin is tapped. If the surface starts to blister or bubble at the edge, the custard is boiling and the oven is too hot.
- And it feels like
Tap the side of the tin. The middle should move as one soft mass rather than rippling like liquid. It will finish setting entirely as it cools.
- Food safety
The filling is a baked egg custard and reaches a safe temperature. Store it in the fridge.
- Where it goes wrong
- Underbaking the base, so the filling soaks in and leaves a pasty layer where the biscuit should be.
- Letting the base cool before the filling goes on, so the two layers separate.
- Baking the filling too hot, which boils the custard, sets it grainy and makes it weep.
- Whisking air into the filling and not skimming the foam, which bakes into a mottled crust.
- Cutting it warm, before the filling has finished setting.
- Dusting with icing sugar hours ahead, so it dissolves into a wet film.
- If it does go wrong
Filling lifts off the base in one sheet: the base was cold when the filling was poured. Wet, pasty layer between the two: the base was underbaked. Grainy filling weeping water: baked too hot, or baked too long. Mottled pale crust on top: foam was not skimmed. Filling did not set: not enough flour, or not enough baking, or the juice was measured generously. Bars will not cut cleanly: not chilled long enough, or the knife was not wiped between cuts.
- Making it ahead
Better made the day before, since it needs two hours of cooling anyway and the flavour settles overnight. Dust with icing sugar at the last moment.
- Keeping it
In the fridge in an airtight box for four days. The base softens slightly by day three, which is unavoidable in any bar with a wet layer on a dry one.
- Reheating
None. Serve cold or cool.
- Freezing
Freezes for two months, cut and separated with paper. Thaw in the fridge and dust with fresh icing sugar, since the first dusting will have dissolved.
- Leftovers
Very good cold from the fridge, which is how most of them are eaten.
- Scaling it
Doubles into a 23 x 33cm tin with about five minutes added to each bake. The proportions scale cleanly.
- Substitutions
Limes work in the same quantity and give a sharper, more floral bar. A mixture of lemon and lime is very good. Cornflour can replace the flour in the filling at 30g rather than 40g and gives a slightly clearer, glossier set.
- Dietary swaps
Contains cereals containing gluten, eggs and milk. Vegetarian, nut free. There is no useful egg-free version: four eggs are the entire structure of the filling.
- Shopping for it
Unwaxed lemons, because the zest of two of them is eaten. If only waxed are available, scrub them hard in hot water first.
- Keeping the cost down
Lemons are cheapest bought loose in a net rather than singly, and the whole recipe needs four. Bottled lemon juice is a real saving and a real loss — the zest is half the flavour and bottled juice has none of it.
- Nutrition
Sugar-heavy, as any set citrus custard is. The acidity makes it read as lighter than it is.
- Worth it?
The sharpest thing in this batch, and the one where the single most important instruction is the least obvious one: pour it on hot.
Where it comes from
- Origin
The United States.
- Also called
Lemon bars, lemon squares, or lemon slice.
- What the name means
Descriptive. Bar refers to the format — a tray-baked sweet cut into rectangles — which is an American category of home baking that includes brownies and blondies.
- History
The bar cookie is an American twentieth-century format: a batter or dough baked in a tray and cut, rather than shaped into individual pieces. Lemon bars appear in American community cookbooks and company baking leaflets from around the middle of the century. The construction — a pressed sweet pastry base under a baked citrus custard — is much older and European, and lemon curds and lemon tarts run through English and French baking from at least the seventeenth century. The bar is an adaptation of the tart to a format that needs no rolling, no tin lining and no blind baking with weights.
- Why it matters
A standard American potluck, bake sale and church supper item, valued precisely because it travels well and cuts into a lot of pieces. Less established in Britain, where the equivalent slot is filled by lemon drizzle cake.
- When it is eaten
None specific. Bake sales, picnics and buffets, because it is a tray of portions rather than a cake to be cut at the table.
- The traditional way
Pouring the filling onto a hot base, which is the technical detail that distinguishes a good bar from a bad one and is often omitted from published recipes.
- How it changed
Modern versions have generally increased the depth of the filling relative to the base, and many use cornflour rather than flour for a clearer set.
- Regional variations
Lime bars, and in the American South key lime versions that shade into key lime pie territory. Coconut and shortbread-with-oats bases both appear.
- How this version differs
The filling goes onto the base hot and the reason is stated, which most published recipes do not do. The lemon is pushed higher and the sugar slightly lower than is usual, and the second bake is at 150C rather than the more common 170C, which is what keeps the set smooth.
- Sources and credit
None available.
Blueberry Muffins
Brown Butter Chocolate Chip Cookies
Carrot Cake
Chocolate Chip Cookies
Chocolate Fudge Cake
Cinnamon Rolls
American
Baking
Desserts
Citrus
Vegetarian