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1
Butter and line a 13 x 9 inch baking pan with buttered parchment or foil.
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2
Position oven rack in middle of oven; preheat to 350u00b0.
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3
In a standing mixer with paddle attachment, beat the butter on medium speed.
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4
Beat in powdered sugar and vanilla; continue beating a minute or two, until light.
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5
Decrease speed and beat in the flour.
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6
Spread the dough over the bottom of prepared pan, using a small offset spatula or the back of a spoon to smooth it.
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7
Bake the base for about 20-25 minutes, until golden and baked through.
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8
While the base is baking, prepare the topping; be careful not to overmix the topping, or it will have a coarse textured foam on the top when baked.
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9
In a big bowl, whisk the eggs just to break them up.
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10
Whisk in the sugar, then the lemon juice and zest.
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11
As soon as the base is baked, remove it from the oven and pour on the topping.
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12
Immediately return pan to oven and keep baking another 25-30 minutes, or until the topping is set and firm.
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13
Cool on a rack until completely cooled.
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14
To cut, use the paper to transfer it to a cutting board and slide a long knife or spatula until it to loosen the paper or foil, then pull away.
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15
Trim the edges, use a ruler to mark, then cut into 2-inch squares.
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16
Dust with powdered sugar before serving.
