Preheat oven to 350 degrees. Line bottom and sides of 13x9 inch pan with heavy-duty aluminum foil, allowing 2 inches to extend over sides; lightly grease foil.
Sit together 1 ¾ cups flour and ½ cup sugar. Cut in butter with a pastry blender or fork until crumbly. Press mixture onto bottom of prepared pan.
Bake at 350 degrees for 20-23 minutes or until lightly browned.
Meanwhile, whisk eggs in a medium bowl until smooth; whisk in next 3 ingredients and remaining 1 ½ cup sugar.
In a separate bowl, stir together baking powder, salt, and remaining ¼ cup flour; whisk into egg mixture. Pour over hot crust.
Bake at 350 degrees for 25 minutes or until filling is set. Let cool 1 hour on a wire rack. Lift from pan, using foil sides as handles. Remove foil and cut into bars. Garnish with powdered sugar if desired.