1 cup broken walnuts

1/3 cup packed light brown sugar

1 teaspoon cinnamon

1/4 cup butter

1/3 cup all-purpose flour

2 large, tart, peeled and sliced apples

2 teaspoons lemon juice

1 3/4 cups all-purpose flour

3/4 teaspoon baking powder
 
1/2 teaspoon baking soda

1/4 teaspoon salt

1/2 cup butter, softened

1 cup granulated sugar

1 teaspoon vanilla

2 eggs

1 8-ounce container sour cream

1/2 cup broken walnuts (optional)

Preheat oven to 350 degrees. Grease a 9-inch springform pan or 9- by 9- by 2-inch baking dish. Combine 1 cup nuts, brown sugar and cinnamon and set aside. For topping, cut the 1/4 cup butter into the 1/3-cup of flour to make coarse crumbs. Stir into that three-quarters of the nut mixture (reserving a third) and set topping aside.

Toss apples with lemon juice; set aside. In a medium bowl, combine the 1 3/4 cup flour, baking powder, soda and salt; set aside. In a large bowl, beat 1/2 cup butter with electric mixer for 30 seconds. Beat in granulated sugar and vanilla. Add eggs, one at a time, beating well after each. Add flour mixture and sour cream alternately to batter. Beat on low speed after each addition until combined.

Spread 2/3 of the batter into the prepared pan. Sprinkle with reserved nut mixture. Lay apples over top. Gently spread remaining batter over apples. Sprinkle with reserved topping. Bake 10 minutes then sprinkle with 1/2 cup more nuts. Bake 45-50 minutes more or until a wooden toothpick inserted in the center comes out clean. If using springform pan, remove side. Cool at least 1 hour. Serve warm with whipped cream, if desired.