Preheat the oven to 350ºF. Combine first three ingredients together in a bowl. Mix with your hands or beat slowly with an electric mixer. Grease a 9-by-13-inch baking dish. Pat mixture into pan. Bake 10 minutes. Meanwhile, mix cinnamon and sugar together and toss with the apples. Remove pan from the oven and top with the apple mixture. Whisk egg and sour cream together and drizzle over the apples. Return to the oven for 30 to 35 minutes. Serve immediately.