Preheat oven to 350°F and line a muffin tin with liners.

In a medium bowl, make the crumb topping by combining all of the topping ingredients (sugar, brown sugar, cinnamon, melted butter, and cake flour). Mix together until crumb topping forms. Set aside.

In the bowl of a countertop mixer with the paddle attached, sift together the dry ingredients for the muffins (cake flour, sugar, baking powder, baking soda, and salt). Stir until well combined.

Add the softened butter and sour cream and mix until combined.

Add the eggs and vanilla and mix just until liquid is absorbed. (It’s ok if the batter looks slightly lumpy.)

Fill the muffin cups about ½ full with batter. (Note: Do not add crumb topping yet.)

Bake the muffins for approximately 23-25 minutes, or until the muffins are set but not quite fully baked. Add a generous amount of crumb topping to the top of each muffin. Press the topping into the muffins gently. Continue baking for another 8-10 minutes, or until muffins are done. (Note: A toothpick inserted into the center of the muffin should come out almost clean once the muffins are done.) Remove from oven and let cool slightly.

While the muffins are cooling, make the Kahlúa Glaze by combining the powdered sugar and Kahlúa together in a small bowl. Stir together until a thick glaze forms.

Once the muffins are slightly cool, drizzle the tops with the Kahlúa Glaze. (Tip: I put the glaze in a sandwich bag and snipped off the corner. It works great as a glazing “tool”!)