2 tablespoons powdered sugar
2 tablespoons granulated sugar
10 tablespoons unsalted butter, softened
1 -1/4 cups all-purpose flour
2 small or 1 large lemon, peel and all, ends trimmed, cut up, seeds removed
4 large eggs
1-1/2 cups sugar
½ cup (8 tablespoons) butter, softened
1 teaspoon vanilla
Grease an 8-x 8-inch pan. Preheat oven to 325°F.
Crust: In a medium bowl, stir together the two sugars. With an electric mixer, beat in the butter until mixture is light and fluffy, about 1 minute. Add vanilla and flour and mix just until incorporated. Pat mixture into the prepared pan and set aside.
Filling: Put all of the ingredients in a blend and puree until smooth. Pour over the shortbread crust.
Bake in the middle of the preheated oven until filling is set, about 45 minutes.
Cool pan on a rack and then refrigerate for 30 minutes before cutting into bars. Sprinkle with more powdered sugar, if desired.