Light or low-fat sour cream, while ideal for topping things, is not ideal in baking recipes. Use regular sour cream in all your baked goods.
Apples & Topping
Preheat oven to 350° F. Cream butter and sugar until smooth. Add eggs one at a time, stirring well after each addition. Add vanilla and stir in sour cream. In a separate bowl, combine dry ingredients and stir into wet ingredients until just incorporated.
In another bowl, combine all ingredients for topping. Toss half of the topping with the sliced apples. Scrape the coffee cake batter into a greased 8-inch round cake pan and level. Cover cake with apples and sprinkle remaining topping over. Bake for 55 to 60 minutes, until a tester inserted in the center of the cake comes out clean.
Serve warm or at room temperature.
Yield: 1 8-inch round cake