This classic coffee cake owes its extra moist texture to the sour cream in the batter. Serve it as part of a brunch buffet or a sweet foil to a vegetable frittata or to complement a berry salad. Unknown source
1Preheat oven to 400. Butter an 8 inch square baking pan.
2In large bowl, whisk together flour, sugar, baking powder and salt. In a medium bowl, whisk egg just til the yolk and while are blended. Add sour cream, milk, and melted butter. Mix well. Pour egg mixture into flour mixture and stir just til ingredients are blended. Stir in the chopped apple. Spread batter evenly in prepared pan.
3to make topping, in a bowl, mix brown sugar, flour and butter. using your fingertips, work ingredients together til a coarse crumbly mixture forms. Add walnuts and mix well with fingertips. Sprinkle topping evenly over batter.
Bake coffee cake til topping is browned and a sharp knife inserted into center comes out clean, about 30 minutes. Let cool for about 5 minutes, then cut into squares and serve warm or at room temperature. Serves 6 to 8