# Classic Lemon Bars

Lemon bars are a sweet, tart lemon custard on a tender shortbread crust. They are a bake sale favorite for a reason: bright, buttery and simple.

The filling uses fresh lemon juice and zest for real flavor, and the crust is pressed in by hand. They cut into 16 neat squares once chilled.

- Total time: 1 h 5 min (prep 20 min, cook 45 min)
- Serves: 16
- Per serving (estimated): 215 kcal, 3 g protein
- Cuisine: American. Category: Dessert. Diet: vegetarian.

## Ingredients

- 225 g unsalted butter, softened (1 cup)
- 65 g powdered sugar (1/2 cup), for crust
- 280 g all-purpose flour (2 1/4 cups), divided
- 1/4 tsp fine salt
- 300 g granulated sugar (1 1/2 cups)
- 4 large eggs
- 180 ml fresh lemon juice (about 4 to 5 lemons)
- 1 tbsp lemon zest
- Powdered sugar, for dusting

## Method

1. Heat the oven to 350°F (175°C). Line a 9x13-inch (23x33 cm) pan with parchment, leaving an overhang on two sides.
2. Beat the butter and 65 g powdered sugar until smooth. Mix in 250 g of the flour and the salt until the dough just comes together.
3. Press the dough evenly into the pan. Prick it with a fork and bake 18 to 20 minutes, until the edges are light golden. Keep the oven on.
4. While the crust bakes, whisk the 300 g granulated sugar, the remaining 30 g flour, the eggs, lemon juice and zest until smooth.
5. Pour the filling over the hot crust.
6. Bake 22 to 25 minutes, until the filling is set and no longer jiggles in the center when you gently shake the pan.
7. Cool completely in the pan on a rack, then chill 1 hour.
8. Lift out using the parchment, cut into 16 bars with a sharp knife wiped clean between cuts, and dust with powdered sugar.

## Why it works

- Pressing the buttery dough into the pan and prebaking it gives a crisp base that does not go soggy.
- Pouring the filling onto the hot crust helps it start setting right away and bonds to the crust.
- Fresh lemon juice and zest give far more flavor than bottled juice.
- A small amount of flour in the filling helps it set firm enough to slice.
- Chilling the bars before cutting gives clean edges.

## The science

- **How the filling sets.** Egg proteins unwind and link together as they heat, trapping the lemon juice and sugar in a soft gel. The flour helps hold it together. The filling is done when it no longer jiggles in the center, about 160°F (71°C).
- **Why prebake the crust.** Raw dough would absorb the wet filling and turn gummy. Baking the crust first sets the starches and dries the surface, so it stays tender and crisp under the custard. The crust should be lightly golden before the filling goes on. A prebaked crust also lifts out cleanly, so the bars slice into neat squares.
- **Why zest and juice both.** Most of the lemon aroma lives in the oils of the zest, not the juice. The juice gives sourness. Using both gives the bars both the tart bite and a fragrant, lemony smell. Zest the lemons before juicing them, since a juiced lemon is hard to zest.

## Tips

- Zest the lemons before juicing them.
- Cool completely before cutting, since warm filling is too soft.
- Dust with powdered sugar just before serving, or it melts into the surface.

## Mistakes to avoid

- Overbaking makes the filling rubbery and browned, so pull the pan when the center no longer jiggles.
- Using bottled lemon juice gives a flat flavor, so squeeze fresh lemons.
- Cutting while warm smears the filling, so chill the bars first.

## Variations and swaps

- Add 1 tbsp of lime zest and swap half the lemon juice for lime juice.
- Add a pinch of ground ginger to the crust.
- Make them with Meyer lemons for a softer, floral flavor.
- Swap powdered sugar in the crust for 50 g granulated sugar for a slightly crisper crust.
- Swap 60 ml of the lemon juice for orange juice to soften the tartness.
- Swap salted butter for the unsalted butter and omit the added salt.

## Storage

Refrigerate the bars in an airtight container for up to 5 days. Freeze cut bars for up to 2 months and thaw in the fridge. Dust with powdered sugar just before serving.

## FAQ

**How do I know when lemon bars are done?**

The edges are lightly golden and the center no longer jiggles when you gently shake the pan. It firms more as it cools. Overbaked bars turn rubbery and brown.

**Why are my lemon bars runny?**

They were underbaked or cut before they were cool. Bake until the center is set and chill for at least 1 hour before slicing.

**Can I use bottled lemon juice?**

You can, but fresh juice tastes much brighter. Bottled juice is often flat or bitter. You need about 4 to 5 lemons for 180 ml of juice.

**Why did my lemon bars turn brown on top?**

The filling baked too long or the oven was too hot. Check at 22 minutes and use an oven thermometer to confirm 350°F (175°C).

**How do I get clean cuts?**

Chill the bars thoroughly and use a sharp knife, wiping it clean with a damp cloth between cuts.

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Source: https://cookingscientist.com/recipes/lemon-bars (Cooking Scientist). Learn the science of cooking in the Cooking Scientist app for iPhone and iPad: https://apps.apple.com/app/id6830326846