1. Pulse 2 cups flour, 1/2 cup powdered sugar, and 3/4 cup butter in a food processor 6 times or until mixture is crumbly. Press mixture into a lightly greased 13- x 9-inch pan.
2. Bake at 350° for 15 to 20 minutes or until lightly golden.
3. Whisk together eggs and next 3 ingredients. Combine baking powder, salt, and remaining 1/4 cup flour; whisk into egg mixture. Pour batter into prepared crust.
4. Bake at 350° for 20 minutes or until set. Cool on a wire rack 2 hours or until completely cool. Cut into squares. Garnish, if desired.