Preheat oven to 325°F. Spray Giant Cupcake Pan with vegetable oil pan spray; set aside.
In medium bowl, combine flour, baking powder and salt; set aside. In large mixing bowl, cream butter and sugar with electric mixer. Add eggs, one at a time, beating thoroughly after each addition. Add zest and extract. Add flour mixture alternately with sour cream; mix well. Stir in rainbow sprinkles. Spoon 4 cups of cake mixture into bottom cavity. Spoon remaining 3 cups of cake mixture into top cavity. Gently tap pan to release any air bubbles.
Bake 60-65 minutes or until cake tester inserted into center comes out clean. Cool in pan 15 minutes. Carefully invert cake onto cooling rack. Cool completely.
Makes about 7 cups batter.