Filling:
2 tablespoons of the cake mixture before the liquid is added. (Cream the sugar, margarine, remove a couple of tablespoons and add a little flour so you have a crumbly mixture) use this: 

2 tablespoons of brown sugar
2 teaspoons of cinnamon
1 cup of finely chopped nuts

Grease a tube or bundt pan. Cream butter and sugar until light and fluffy. Stir flour and baking powder together (set aside). Mix milk and vanilla extract. (Set aside). Add eggs one at a time, beating 1 minute after each addition, beat 3 minutes more. At low speed, add dry ingredients, alternate with milk, beginning and ending with dry ingredients. Add sour cream and mix well. Pour about 2/3 into pan. Sprinkle filling over the batter in the pan, fill pan with remaining cake mixture, and bake until done about 45 to 55 minutes. Actually you can use any yellow cake recipe and just add sour cream to it, then proceed with the filling, etc.  To make a delicious pound cake, omit the sour cream and the filling, and add almond extract to the milk and vanilla extract.