Preheat oven to 350 degrees F
In a large bowl mix together, cake mix, eggs, butter, sour cream, and vanilla. Use a stand or hand mixer on high until thoroughly blended.
In a small bowl mix together the topping/filling.
Grease and flour a 9 inch square cake pan.
Spoon half of the cake mix into the cake pan.Smooth out with the back of a spoon. Sprinkle the cake with 1/2 of the topping mixture.
Spoon the other half of the cake mix in the cake pan and finish by sprinkling the last half of the topping mixture.
Bake for 45-50 minutes or until toothpick inserted in the center comes out clean.