Apple Walnut Coffee Cake

Make the walnut topping: In a bowl, combine walnuts, brown sugar, cinnamon, and flour. Add the butter and crumble between your fingertips until the mixture forms coarse crumbs. Refrigerate mixture while preparing the cake batter.

Make the apple cake: Preheat oven to 350F. Grease and flour the bottom and sides of a 9- by 13-inch rectangular cake pan or a 10-inch springform pan.

Sift together the flour, baking soda, baking powder, and salt.

In the bowl of an electric mixer, cream together butter and sugar until the mixture becomes light. Beat the eggs one at a time, beating well after each addition. Add the vanilla and lemon zest.

At lowest speed of the mixer, beat in flour mixture alternately with the sour cream.

Fold in apples by hand just until evenly distributed in the batter.

Pour into prepared baking pan. Sprinkle the top evenly with the prepared walnut mixture.

Bake for approximately 40 to 50 minutes for a rectangular pan and 45 to 55 minutes for a 10-inch springform pan or until a toothpick inserted into the center of the cake comes out clean.