INSTRUCTIONS
1. Prepare the white cake according to the directions on the box, adding the sour cream and vanilla.
2. Bake in a 10 inch round baking pan and cool the cake completely.
3. For the lemon cream filling, mix the mascarpone, powdered sugar, lemon juice, lemon zest of half the lemon and whipping cream, then mix until creamy and smooth.
4. For the crumb topping, combine ¾ cup of the lemon cake mix with the melted butter to make a crumb topping.
5. To assemble the cake, cut the white cake in half to spread the lemon cream filling between the two layers of white cake. Frost the top of the cake with a thin layer of cream filling and sprinkle the crumb topping.
