Streusel Apple Coffee Cake

Step 1
Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9- or 10-inch Bundt pan.

Step 2
Make streusel: Mix together brown sugar, flour, and cinnamon in a medium bowl. Cut in butter with a fork until crumbly. Stir in walnuts and set aside.

Step 3
Make cake: Stir together flour, baking powder, and baking soda in a medium bowl; set aside. Cream together sugar and butter in a large bowl until light and fluffy. Beat in eggs, one at a time, mixing well after each addition. Stir in yogurt and vanilla. Stir in flour mixture just until blended.

Step 4
Pour 3 cups batter into the prepared Bundt pan. Sprinkle with 1/4 of the streusel, then layer with apples. Sprinkle with 1/2 of the remaining streusel. Pour in remaining batter and top with remaining streusel. Lightly pat down top layer of streusel into batter.

Step 5
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 50 to 60 minutes. Cool in the pan on a wire rack for 15 minutes. Place cookie sheet over the pan and carefully invert both. Remove Bundt pan; let cake cool completely.