Mix together the flour, baking powder, sugars, milk, sour cream, vanilla, and eggs on low speed until combined. Slowly drizzle in melted butter and mix on low until butter is incorporated into the batter.
Pour batter into a 9x13 baking pan that's been prepared with baking spray or greased and lightly floured.
Mix topping ingredients together well. Spoon dollops of mixture on top of cake batter, and swirl in with a knife.
Bake for 35-45 minutes, or until a tester comes out with moist crumbs. (Filling mixture will still be slightly wet.)
While cake is baking, combine caramel ingredients in a medium saucepan, and bring to a slow simmer stirring frequently. Lightly simmer for 5 minutes, and remove from heat and set aside.
Remove cake from oven and let cool for 10 minutes. Pour caramel sauce over cake.
Let cake cool completely. Mix together glaze ingredients until no lumps remain, and drizzle over cake.