The Crumbiest Coffee Cake

Prepare the Cake: Preheat oven to 350 degrees F. Grease and flour 13-inch by 9-inch by 20-inch metal baking pan. In bowl, stir together flour, baking powder, baking soda, cinnamon, and salt. In large bowl, with electric mixer, cream butter with both sugars on medium speed until light and fluffy. Beat in eggs, 1 at a time, beating well after each addition. Beat in vanilla. Alternately fold dry ingredients and sour cream into batter, beginning and ending with dry ingredients. Scrape batter into pan and smooth top. Prepare the Topping: In medium bowl, with pastry blender or 2 knives, cut together sugar, flour, butter, and cinnamon until mixture resembles coarse crumbs. Stir in nuts. Sprinkle topping evenly over batter. Bake cake 45 to 50 minutes, or until toothpick inserted in center comes out just clean (its OK if there are some crumbs clinging to the toothpick; you don't want the cake to be too dry). Cool in pan on wire rack. Store, covered, in refrigerator up to 3 days.