Perfect Lemon Bars

From Cook's Illustrated. The lemon filling must be added to a warm crust.

Crust:
1-3/4  cups  flour
2/3   cup  powdered sugar
1/4  cup  cornstarch
3/4  tsp  salt
12  Tbs  unsalted butter, cold and cut into 1" pieces

Lightly butter a 9x13" baking pan, and line it lengthwise with a sheet of parchment or waxed paper. Dot paper with butter, and then lay a second sheet of paper over it crosswise.

Pulse flour, powdered sugar, cornstarch, and salt in a food processor. Add butter and process 8-10 seconds. Then pulse it until mixture resembles coarse cornmeal, about 3 or more 1-second pulses. Sprinkle mixture into lined pan. Press down with fingers firmly to spread and compact over entire pan, and 1/2" up the sides. Chill for 30 minutes, and then bake @350 for 20 minutes.

Filling:
4  large  eggs, beaten lightly
1-1/3  cups  sugar
3  Tbs  flour
1/8   tsp  salt
2  tsp  finely grated lemon zest
Juice from  2  lemons
1/3  cup  whole milk

Reduce oven temp to 325 degrees. Whisk eggs, sugar, and flour. Stir in lemon juice, milk, and salt. Pour filling mixture into warm crust. Bake @325 until it feels firm when touched lightly, about 20 minutes.

Cool on a wire rack until near room temp, at least 30 minutes. Grasp the lengthwise edges of the paper and lift the bars out of the pan, onto a cutting board. Cut into squares using a pizza cutter, and wiping the blade clean after each cut. Sift powdered sugar over the tops of bars.