Sour Cream Coffee Cake Muffins

Preheat the oven to 375 degrees F (190 degrees C). Grease or line a 12-cup muffin tin with paper liners.

Combine brown sugar, walnuts, and cinnamon in a bowl for the filling/topping.

Beat butter, sugar, and eggs together in a large bowl with an electric mixer on medium speed until creamy. Add sour cream and vanilla extract and combine well.

Whisk flour, baking powder, baking soda, and salt together in a small bowl. Add to the butter mixture and combine well.

Spoon 1 tablespoon of batter into each prepared muffin cup. Sprinkle 1 teaspoon of filling mixture in the middle of each muffin and top with 1 tablespoon of batter. Sprinkle remaining walnut mixture on top.

Bake in the preheated oven until a toothpick inserted into the center of a muffin comes out clean, about 25 minutes. Remove from the pan and cool on a wire rack.