Grease a 9-inch pie plate. For streusel topping, in a medium bowl, stir together the 2/3 cup flour, oats, brown sugar and cinnamon. Using a pastry blender, cut in the 1/3 cup butter until mixture resembles coarse crumbs. Stir in chocolate pieces and dried cherries. Set aside.
In a bowl, stir together the 1 cup flour, whole wheat flour, baking powder, baking soda and salt. In a large mixing bowl, beat the 1/2 cup butter with an electric mixer for 30 seconds. Add granulated sugar and beat until fluffy. Add eggs and sour cream; beat until combined.
Add flour mixture and beat on low speed until just combined. Spread half of the batter into pie plate. Sprinkle with half of the streusel mixture. Spread on remaining batter and top with remaining streusel topping. Cover and refrigerate for 4 to 24 hours.
Uncover. Tent with foil and bake in a 350 degree F oven for 30 minutes. Uncover and bake for 20 to 30 minutes or until a toothpick inserted near the center comes out clean. Serve warm. Makes 8 servings.