In a medium bowl, combine 2 c. flour and baking powder. Set aside.
In a medium mixing bowl, cream butter and brown sugar.
Blend in sour cream, caramel topping, and milk and mix until smooth. Stir in egg and vanilla.
Add dry ingredients and mix just until blended.
Fold in apples.
Spoon batter into a 10 inch springform pan and sprinkle with crumble topping (see below).
Bake at 350 degrees for 50-60 minutes or until center is set and top is golden brown.
Remove from oven and cool.
Drizzle with caramel topping before serving.