Preheat oven to 350F.
Place cups of flour in a food processor. Add butter and powdered sugar and pulse until mixture looks like coarse meal. Press into the bottom of a roughly 12 x 8 inch baking pan. Bake 20 to 25 minutes.
Beat eggs with a mixer. Add sugar; blend well. Add lemon juice and remaining tablespoons of flour; beat well. Add baking powder and lemon rind; beat well. Pour over hot crust (do not let it cool). Bake 30 to 35 minutes. Sprinkle top with additional powdered sugar. Serves 24.
