Citrus Bars

Ingredients

• 1 cup all-purpose flour
• 1/3 cup nonfat sour cream
• 3 tablespoons powdered sugar
• 3 tablespoons unsalted butter, room temperature
• 3 eggs
• 3 egg whites
• 1/2 cup orange juice
• 1/2 cup lemon juice
• 1 tablespoon lemon zest, grated
• 1/4 teaspoon baking powder
• 1 1/2 cups powdered sugar (again)