Streusel Coffee Cake

Streusel topping 2/3 cup all-purpose flour 1/3 cup light brown sugar, packed 1/3 cup granulated sugar1 teaspoon ground cinnamon 1/4 teaspoon ground allspice6 tablespoons cold unsalted butter, cut into small pieces1 1/4 cups walnuts, choppedCoffee cake2 1/4 cups all-purpose flour1 teaspoon baking powder 1/2 teaspoon baking soda6 tablespoons unsalted butter, softened 1/2 cup light brown sugar, packed 1/2 cup granulated sugar2 large eggs2 teaspoons vanilla extract1 cup low-fat buttermilkGlaze1 cup powdered sugar1 teaspoon vanilla extract1 1/2 tablespoons milkHeat oven to 350 degrees. Lightly grease bottom of an 8-inch square baking pan.For the topping: In medium bowl, stir flour, sugars and spices together. Using pastry blender, two knives or fingertips, work cold butter into dry ingredients. Stir in walnuts. Cover and chill while preparing batter.For the batter: In a medium bowl, whisk together the flour, baking powder and baking soda. Set aside.In a large bowl, beat butter and sugars on low speed until combined. Increase speed to medium and beat 1 minute until smooth. Add eggs and vanilla. Beat additional 1 minute until smooth. Scrape bowl well.Add half the flour mixture and 1/2 cup buttermilk to the creamed mixture. Beat on low speed 30 seconds. Scrape bowl. Add remaining flour mixture and 1/2 cup buttermilk. Beat on medium speed one minute until smooth. Scrape bowl well.Spoon half of the batter into baking pan; smooth with spoon. Sprinkle half the topping over batter. Carefully spoon remaining batter over topping. Spread with spoon to edges of pan. Sprinkle with remaining topping. Bake 50-55 minutes; tester inserted at center of cake should come out clean when cake is done. Cool completely.For the glaze: In small bowl, stir together powdered sugar, vanilla and milk until smooth and drizzly consistency. Add a few drops of additional milk if needed. Drizzle over cooled coffee cake.Serves 12.Baker's hint: For a softer crunch in the topping, substitute pecans for the walnuts.Nutrition values per serving: 447 calories, 20 g fat (8 g saturated), 60 g carbohydrates, 2 g fiber, 8 g protein, 67 mg cholesterol, 134 mg sodium.