Lemon Bars

Before you start

Lemon bars pair a pressed shortbread crust with a filling of eggs, sugar, lemon juice and a little flour that bakes into a tart, sliceable curd. The balance should lean sharp: there is a lot of sugar, but enough fresh lemon juice and zest that the filling tastes bright rather than candied.

Two details make a clean, glossy filling. First, pour it onto the crust while the crust is still hot from the oven, which helps the layers bond and keeps the base crisp. Second, bake the filling at a lower temperature than the crust so it sets gently without puffing and forming bubbles. The bars need a full chill before cutting; warm curd smears and the crust crumbles.

Ingredients

• Shortbread crust225 g (1 cup) unsalted butter — softened
• 65 g (½ cup) powdered sugar
• ¼ tsp fine salt
• 250 g (2 cups, spooned and leveled) all-purpose flour
• Lemon filling6 large eggs — room temperature
• 400 g (2 cups) granulated sugar
• 40 g (⅓ cup) all-purpose flour
• 180 ml (¾ cup) freshly squeezed lemon juice — from 4 to 5 lemons
• 1 tbsp finely grated lemon zest
• pinch fine salt
• Finish2 tbsp powdered sugar — for dusting

Method

1. Heat the oven to 175°C (350°F). Line the pan with parchment, leaving an overhang on the long sides.
2. Beat the butter, powdered sugar and salt until smooth. Add the flour and mix on low until the dough forms moist clumps.
3. Press the dough evenly into the pan with your fingers or the base of a measuring cup. Prick it all over with a fork and bake for 18 to 22 minutes, until the edges are golden and the center is light golden.
4. While the crust bakes, whisk the eggs, sugar and flour until smooth, then whisk in the lemon juice, zest and salt. Strain the mixture through a sieve to remove the zest strands and any foam if you want a perfectly smooth top. Skim off bubbles.
5. When the crust comes out, lower the oven to 160°C (325°F). Pour the filling over the hot crust right away.
6. Bake for 20 to 25 minutes, until the filling is set at the edges and the center barely jiggles when you nudge the pan. If you check with a thermometer, the center should read at least 71°C (160°F).
7. Cool on a rack for 1 hour, then refrigerate for at least 2 hours, until firm and cold.
8. Lift out the slab, trim the edges if you like, and cut into 24 bars with a long knife wiped clean between cuts. Dust with powdered sugar just before serving.

Tips for success

• Dust with powdered sugar only right before serving. The moist filling dissolves it within an hour.
• Roll the lemons on the counter before juicing and zest them first; zesting a juiced lemon is much harder.
• For a thicker filling layer, use a 23 cm (9 in) square pan with half the crust and two thirds of the filling, and bake the filling a little longer.

Substitutions

Lemon juice

Meyer lemons make a sweeter, more floral bar; reduce the sugar by 50 g. Lime juice gives a key lime-style bar.

Powdered sugar in the crust

Granulated sugar works at 50 g, but the crust will be slightly crunchier and less fine.

All-purpose flour in the filling

Use 2 tbsp cornstarch for a slightly more translucent, silkier filling.

Variations

Grapefruit bars

Replace 120 ml of the lemon juice with fresh pink grapefruit juice and use grapefruit zest.

Brown butter crust

Brown the crust butter, chill it until solid, then use it softened as directed.

Troubleshooting

Filling has a foamy, bubbly top layer

Too much air was whisked in or the oven was too hot. Whisk gently, skim the foam, and bake the filling at 160°C (325°F).

Filling seeped under the crust

The crust was underbaked or had cooled and cracked. Bake it to light golden and pour the filling on while it is hot.

Filling is runny after chilling

It was underbaked. Next time bake until only the very center wobbles; the edges should look set and matte.

Filling tastes eggy

It overbaked and started to curdle, or the lemon was weak. Pull the pan at the barely-jiggly stage and use fresh juice and zest.

Storage

Lemon bars contain a lot of egg, so keep them refrigerated in a covered container for up to 4 days. Do not leave them out more than 2 hours (1 hour above 32°C / 90°F). Freeze undusted bars for up to 2 months; thaw in the refrigerator.

Safety notes

The filling is an egg dish; bake it until set, about 71°C (160°F) in the center. Do not taste the raw filling or crust dough. Contains egg, wheat and milk.