In a medium bowl sift together flour, baking powder, and salt. In another medium bowl mix milk and sour cream. Set bowls aside.
Pour the batter into prepared pan and smooth the top. Sprinkle crumble evenly over the batter. It will look like a lot of crumbs, but use them all. Bake for 40-50 minutes or until a toothpick inserted into the center of the cake comes out clean. Allow cake to cool completely.