In a medium bowl combine the all-purpose flour, brown sugar, cinnamon and salt. Add melted butter and mix until well combined. Use clean hands to break into crumbs. Set aside.
Cream the butter and sugar. Mix in the eggs and vanilla extract. Fold in half of the dry ingredients then add all of the buttermilk. Fold in the remaining dry ingredients.
Pour the cake batter the prepared pan. Top with the diced apples then sprinkle on the crumb topping. Bake the crumb cake then drizzle with caramel sauce once cooled.