Preheat the oven to 350°F. Grease a 9-inch springform pan or an 8x8-inch square baking pan.
In a bowl, cream together the butter, sugar, and egg yolk.
Add the flour, baking powder, and milk, and mix well.
Spread the dough to cover the bottom of the pan.
Bake for 10 minutes. Remove the cake from the oven and let it cool in the pan, but keep the oven at 350°F.
Once the cake has cooled, sprinkle with confectioner’s sugar.
Mix all the apple filling ingredients together in a bowl.
Spread this mixture over the cooled cake in the pan.
Butter Crumb Topping
Mix all the butter crumb topping ingredients together in a bowl.
Spread the topping over the apple filling in the pan.
Bake for about 1 hour. To test for doneness, insert a toothpick and if it comes out clean it is done, if the toothpick comes out with batter on it, place back into the heated oven and cook for an additional 5 minutes before testing again.