• Preheat the oven to 350°.
• Prepare a 12 portion muffin pan with paper liners or spray with a nonstick baking spray.
• In a bowl with a mixer, cream together the butter and sugar until smooth.
• Add in the egg and mix on medium until combined.
• Add in the banana, blend on medium-low, and then add in the sour cream and mix until combined.
• Next, add in the vanilla, cinnamon, flour, baking soda, and salt.
• Mix on medium until all ingredients are incorporated.
• Portion out 3 tablespoons of batter into each muffin compartment.

Crumb topping Mix the butter, flour, and sugar until it resembles coarse crumbs, use a fork. Then pile a heaping tablespoon of crumb topping into the batter of each muffin.

• Place the filled muffin pan into the preheated oven.
• Bake at 350° for 25 minutes, or until a toothpick comes out clean.
• Remove pan from oven, allow to cool for 5 minutes then remove muffins from pan and cool on a wire tack or serve warm.