Sour Cream and Blueberry Coffee Cake with Streusel

Preheat oven to 350°F. Grease a 9-inch bundt pan well. Set aside.

Make the streusel: combine all ingredients in a bowl. Mix until mixture resembles wet sand. Set aside.

Make the coffee cake: whisk together eggs, 1 cup sour cream, and vanilla extract in a medium bowl. Set aside.

In the bowl of an electric mixer fitted with the paddle attachment, sift together flour, baking powder, baking soda, and salt. Add butter, sugar, and remaining sour cream. Beat until mixture resembles wet sand, about 11/2 minutes.

Add the egg mixture in 3 batches, beating well after each addition. Beat until batter is light and fluffy, about 1 minute.

Sprinkle 3/4 of the streusel on the bottom of the prepared pan. Pour in 2 cups of the cake batter. Spread blueberry filling, and top with orange zest. Sprinkle with remaining streusel mixture and pour in the rest of the cake batter.

Bake for 50 to 60 minutes, or until a cake tester inserted in the cake comes out clean. Remove cake from pan and cool completely on a wire rack. Garnish with finely chopped walnuts.