Preheat oven to 350 degrees and generously butter a 9-by-13-inch baking pan.

Cream butter and sugar together until light and fluffy. Add eggs one at a time, beating well after each addition. Add vanilla extract.

In a separate bowl, sift flour with baking powder, baking soda and salt. With the mixer on low speed, add the flour mixture to the butter mixture alternately with sour cream until just combined. Do not overmix. Pour batter into prepared baking pan.

Make the topping: Combine sugar, cinnamon, flour and nuts in a small bowl and mix well.

Sprinkle the topping evenly over the cake and tap surface to evenly it up. Bake 30 to 35 minutes, or until a cake tester comes out clean.

Cool, cut into pieces and serve.