Banana Flip Cake

1 (18.25 ounce) box yellow cake mix
1 small box instant banana pudding mix
4 eggs
1 1/2 cups milk
1 1/2 cups granulated sugar
1/4 cup all-purpose flour
3/4 cup butter
3/4 cup shortening
3/4 cup milk
1 1/2 teaspoons banana extract

Preheat oven to 350 degrees F. Grease and flour two 13 x 9-inch pans.

In a large bowl, stir together the cake mix and instant pudding. Beat in the eggs and the 1 1/2 cups of milk. Divide the batter evenly between the two pans.

Bake 15 to 17 minutes, or until a wooden pick inserted into the cake comes out clean. While the cake is baking, make the filling.

Stir together the sugar and flour. In a medium bowl, cream together the butter, shortening and sugar mixture. Beat in the milk and banana extract until smooth.

When the cake is cooled, invert onto a serving tray. Spread filling over the top and cover with remaining layer of cake. Keep chilled until 1/2 hour before serving.