• 1 tsp. grated lemon zest
Preheat oven to 350 degrees and get out an 8-inch square baking pan.
To make the crust: Beat the butter and powdered sugar together until blended, then add the lemon zest, flour and salt, and mix thoroughly. Press the mixture evenly in the bottom of the baking pan and bake for 20 minutes. Remove from the oven and cool on a rack.
To make the filling: Beat together the eggs, granulated sugar, flour, lemon juice and lemon zest until thoroughly blended. Pour over the crust and return to the oven to bake for 20 to 25 minutes, until the top is dry and barely browned around the edges -- don't overbake; the custard filling should remain soft.
Remove from the oven and cool on a rack, then cut into 2-inch squares. If you wish, sift powdered sugar over the top before serving.