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1
Heat the oven to 350F and arrange a rack in the middle.
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2
Coat a 13-by-9-inch baking dish with butter; set aside.
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3
Place 2 cups of the flour, the powdered sugar, and 1/2 teaspoon of the salt in the bowl of a food processor fitted with a blade attachment and pulse briefly to combine.
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4
Scatter butter pieces over flour mixture and pulse until dough just begins to come together, about 20 (1-second) pulses.
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5
Crumble dough into the prepared baking dish and, using the base of a measuring cup or a glass dipped in flour, press evenly into the pan.
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6
Bake until crust is fully set and just starting to brown on the edges, about 25 minutes.
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7
Remove from the oven and let cool while you make the filling, at least 5 minutes.
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8
Reduce the oven temperature to 325F.
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9
To make the filling, combine remaining 3 tablespoons flour, remaining 1/2 teaspoon salt, granulated sugar, and eggs in a large bowl and whisk until sugar is dissolved and mixture is smooth, about 2 minutes.
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10
Add lemon juice and zest and whisk until well combined.
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11
Pour filling over baked crust, return to the oven, and bake until set, about 25 to 35 minutes.
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12
Remove from the oven and let cool on a wire rack.
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13
Cut into squares and serve.
