1. In a food processor or a bowl, whirl or stir flour and 1/2 cup powdered sugar until blended. Add butter and whirl or rub in with your fingers until dough holds together when squeezed. Press evenly over the bottom of a 9- by 13-inch pan.
2. Bake in a 350° regular or convection oven until crust is golden brown, 20 to 25 minutes.
3. Meanwhile, in a bowl with a mixer on medium speed or a whisk, beat eggs to blend with granulated sugar, lemon peel, lemon juice, baking powder, and salt. Stir in blueberries.
4. Pour egg mixture into pan over warm crust. Return to oven and bake until filling no longer jiggles when pan is gently shaken, 20 to 25 minutes. Sprinkle lightly with powdered sugar and let cool at least 15 minutes. Serve warm or cool. If making up to 1 day ahead, wrap airtight when cool and chill. Cut into about 2-inch squares and lift out with a spatula.
Nutritional analysis per square.