Sour Cream Coffee Cake

Preheat the oven to 350 degrees. Make the topping: In a small bowl combine 1/2 cup sugar, cinnamon, vanilla, and walnuts; set aside.

Make the cake: Butter and flour a 9-inch springform pan; set aside. In a medium bowl, whisk together flour, baking powder, baking soda, and salt; set aside.

In the bowl of an electric mixer fitted with the paddle attachment, beat together butter, sugar, and eggs until smooth. Add the flour mixture alternating with the sour cream, beginning and ending with the flour mixture.

Spread half of the batter into the prepared baking pan, and sprinkle with half of the topping. Repeat with remaining batter and topping.

Bake until a cake tester inserted in the center comes out clean, 25 to 30 minutes. Cool for 15 minutes, then remove sides of pan and place on a wire rack to cool completely. Serve topping side up.