Preheat oven to 350 degrees. Butter two 8 inch square cake pans. In a large mixing bowl, beat butter with sugar until well blended. Add eggs, one at a time and beat well. Add sour cream and mix thoroughly. In a small bowl, mix together 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 cherry preserves. Spread batter in pans. Bake 20 to 30 minutes, or until a toothpick inserted in the center comes out clean.