1 (18-1/4 ounces) lemon cake mix with pudding
4 eggs
2 tablespoons vegetable oil
1 cup buttermilk
1/2 cup butter, melted
3/4 cup sugar
1 teaspoon vanilla
Preheat oven to 350 degrees. Reserve 1 cup dry cake mix and set aside. In a large bowl, combine remaining cake mix, 1 egg and oil; blend well. Press batter into bottom of greased 13-by-9-inch pan.
In a medium bowl, beat remaining eggs, buttermilk, butter, sugar and vanilla until well blended. Slowly add reserved cake mix and beat on medium speed until mixture is smooth, about 2 minutes.
Pour over batter crust in cake pan and bake for 35 to 40 minutes, until lightly browned on top. Cool and cut into bars.
