Preheat oven to 350~. Butter 2 (8") square cake pans. In a large mixer bowl, beat butter with sugar until well combined. Add eggs 1 at a time and beat well. Add sour cream and mix thoroughly. In a small bowl, mix together the flour, baking powder, baking soda and salt. Add the dry ingredients to the butter mixture. Batter will be stiff. Stir in the vanilla, zest and preserves. Spread batter in pans. Bake 20-30 minutes or until an inserted toothpick comes out clean.