Preheat oven to 350°F (175°C) and line a muffin tin with paper liners.
In a bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon.
In another bowl, mix melted butter and brown sugar until smooth.
Add eggs, sour cream, milk, and vanilla extract. Mix well.
Gradually fold in the dry ingredients until just combined.
Mix chopped pecans, brown sugar, and melted butter in a small bowl for topping.
Fill muffin cups ¾ full, then add topping and press a pecan half on each.
Bake for 18–22 minutes or until a toothpick comes out clean.
Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.