Classic Lemon Bars

Instructions

1. 1

   Heat the oven and line the pan

   Set a rack in the middle of the oven and heat it to 350°F. Line a 9x13-inch metal pan with two strips of parchment running in opposite directions, letting a couple of inches hang over the long sides. Those flaps are your handles later, so don't skip them. Metal is better than glass here, since glass holds heat and tends to overcook the edges of the filling before the center sets.

2. 2

   Zest and juice the lemons first

   Zest the lemons before you cut them, and take only the yellow part of the peel. You need 3 tablespoons of zest total, 1 for the crust and 2 for the filling, so keep them separate. Then juice the lemons and pour the juice through a fine strainer to catch seeds and pulp. Measure after straining, since pulp can throw off the volume.

3. 3

   Mix and press the crust

   Whisk the flour, powdered sugar, salt, and 1 tablespoon of zest together in a medium bowl, rubbing the zest into the dry mix with your fingertips to release its oils. Pour in the melted butter and vanilla and stir with a fork until no dry flour is left and the dough clumps when you squeeze it. Scatter it over the lined pan and press into an even layer, using the flat bottom of a measuring cup to compact it. Work it a little way up the corners so the filling has a tidy edge to sit against.

4. 4

   Blind-bake the crust

   Bake for 20 to 24 minutes, until the surface looks dry and matte rather than shiny and the edges are a light golden brown. An underbaked crust is the main cause of a soggy bottom layer, so give it the full time. Leave the oven on and keep the pan out on a rack while you mix the filling, but work quickly because you want the crust still hot when the filling goes on.

5. 5

   Whisk the filling

   In a large bowl, whisk the granulated sugar, flour, and salt together so the flour is evenly dispersed and won't clump. Add the eggs and whisk until smooth and pale, about a minute. Whisk in the remaining 2 tablespoons of zest and the lemon juice. Mix this right before you pour it. If the acidic juice sits on the eggs for a long time it starts to tighten them, and you'll get a grainy layer.

6. 6

   Pour over the hot crust and bake

   Pour the filling over the hot crust and slide the pan straight back into the oven. Bake 25 to 30 minutes, until the surface has lost its wet sheen and the center jiggles as one soft unit when you nudge the pan, like set gelatin rather than liquid. The filling firms up considerably as it cools, so pull it while there's still a little wobble. A thin pale foam on top is normal and will settle.

7. 7

   Cool, then chill

   Cool the pan completely on a wire rack, 1 to 2 hours, then refrigerate for at least 2 hours or overnight. This is not optional if you want clean squares. Warm lemon bars smear no matter how sharp your knife is.

8. 8

   Cut and dust

   Lift the slab out by the parchment onto a cutting board. Cut into 24 bars with a long thin knife, wiping the blade clean between every single cut. Dust with powdered sugar through a fine sieve just before serving, since the sugar dissolves into the filling within an hour or two.

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Baker's Tips

• 1.

  Use fresh lemons, not bottled juice. Bottled juice is pasteurized and tastes flat and slightly metallic in a filling this lemon-forward, and you lose the zest entirely.

• 2.

  Rub the zest into the sugar or flour with your fingertips. It takes ten seconds and releases the citrus oils, which carry far more lemon aroma than the juice does.

• 3.

  If you want a sharper, more tart bar, cut the granulated sugar to 1 3/4 cups. Going lower than that starts to affect how the custard sets.

• 4.

  For picture-perfect tops, skim off any surface foam with a spoon right after pouring the filling into the pan.

• 5.

  A pale, undercooked line where the crust meets the filling usually means the crust cooled down before the filling went on. Pour while the crust is still hot and the two layers fuse.

• 6.

  Freeze the cut bars on a tray for 20 minutes before packing them for a potluck. They travel without sticking to each other and thaw in about 30 minutes.

Equipment

• 9x13-inch metal baking pan
• Parchment paper
• Microplane or fine grater
• Citrus juicer or reamer
• Fine-mesh strainer
• Large mixing bowl
• Whisk
• Wire cooling rack

Storage