- Prep
- 20 min
- Cook
- 45 min
- Total
- 65 min
- Serves
- 12
Ingredients
What you’ll need — tap to tick off as you go
- 230 g
- 50 g
- 170 g
- 1 g
- 250 g
- 1 g
Process
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Heat the oven to 180°C. Grease a 20 x 20 cm square baking tin with a little unsalted butter and line it with baking paper, leaving an overhang on two sides.
In a bowl, rub 170 g softened unsalted butter into 200 g plain flour and 50 g icing sugar with your fingertips until the mixture looks like fine breadcrumbs. Add 1 g salt and press the mixture firmly and evenly into the base of the tin.
Bake the shortbread base for 18 to 20 minutes, until pale gold at the edges. Remove from the oven and leave to cool for 10 minutes while you make the filling. Keep the oven on.
Zest 2 of the lemons into a large bowl, then squeeze 120 ml juice from the lemons and set aside. Add 4 eggs and 250 g caster sugar to the zest and whisk for 1 minute, until smooth and slightly pale.
Sift 30 g plain flour and 1 g baking powder into the egg mixture, then pour in the 120 ml lemon juice. Whisk gently until completely combined, trying not to whip in too much air.
Pour the lemon filling over the warm shortbread base and return the tin to the oven. Bake for 20 to 25 minutes, until the filling is set at the edges but still has a slight wobble in the centre.
Cool completely in the tin on a wire rack, about 1 hour, then refrigerate for at least 2 hours before lifting out and cutting into 12 squares. Dust with icing sugar just before serving.
Kitchen notes
Kitchen notes
- The most common mistake is underbaking the filling: it should be set at the edges with only a faint wobble in the middle when you nudge the tin. If it still sloshes, give it 5 more minutes.
- Pour the filling over the base while the base is still warm. This helps the layers fuse so the topping does not separate or slide off when cut.
- Chill the bars thoroughly before slicing. A cold, firm filling cuts into clean squares; a warm one smears. Wipe the knife between cuts for neat edges.
- Do not over-whisk the filling after adding the flour. Too much air makes the top puff and crack instead of staying smooth and glossy.
Substitutions
- lemons→an equal mix of lemon and lime juice and zest for a sharper flavour
- caster sugar→granulated sugar blitzed briefly in a blender so it dissolves easily
- unsalted butter→the same weight of salted butter, omitting the 1 g added salt
- plain flour→gluten-free plain flour blend for a gluten-free version
Storage & reheating
Store cut lemon bars in an airtight container in the fridge for up to 4 days, separating layers with baking paper. They can be frozen for up to 2 months, wrapped individually; thaw in the fridge overnight. Serve cold or at room temperature, and dust with fresh icing sugar just before serving since it dissolves into the surface over time.
FAQ
The questions we get asked most
Why is my lemon filling runny?
The usual cause is underbaking or too much lemon juice relative to the eggs and flour. Bake until the edges are set and the centre only wobbles slightly, then chill for at least 2 hours so it firms up. Measuring the juice rather than squeezing freehand keeps the ratio reliable.
Why did my lemon bars crack on top?
Cracks come from over-whisking the filling, which traps air that expands in the oven, or from baking too long. Whisk gently once the flour goes in and pull the tin when the centre still has a slight wobble. A dusting of icing sugar hides small cracks anyway.
Can I make lemon bars ahead of time?
Yes. Bake them up to 2 days ahead, cool, and refrigerate covered in the tin. Add the icing sugar only on the day of serving, because it dissolves into the surface within a few hours. They also freeze well for up to 2 months.
Can I use bottled lemon juice instead of fresh lemons?
Fresh juice gives the best flavour, but bottled works in a pinch. Use 120 ml and add the zest of 1 fresh lemon if you have one, since bottled juice has little aroma. Bottled juice can be slightly more acidic, so taste the filling before baking.
How do I know when the lemon bars are done?
The edges should look set and slightly puffed, while the centre jiggles gently like set jelly when you nudge the tin. A skewer inserted 2 cm from the edge comes out clean. If the whole surface ripples, bake 5 more minutes and check again.
Why is my shortbread base soggy?
The base was likely underbaked before the filling went on, or the bars were stored before cooling completely. Bake the base until pale gold at the edges, and always cool the bars fully, then chill, before covering. Condensation under a lid is the other culprit.
Can I double this recipe for a larger tin?
Yes, use a 23 x 33 cm tin and keep the oven at 180°C. The base takes about 22 minutes and the filling 25 to 30 minutes. Check early, since a larger volume of filling can set faster at the edges than you expect.
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