Preheat your oven to 350°F (175°C) and prepare a muffin tin by lining it with paper liners or greasing each cup.

In a medium bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, and cinnamon.

In a large bowl, combine the melted butter and light brown sugar, stirring until smooth. Add the eggs, sour cream, whole milk, and vanilla extract, mixing well.

Gradually fold the dry ingredients into the wet batter using a spatula until just combined.

In a small bowl, mix the finely chopped pecans with some brown sugar and melted butter for the topping.

Spoon the muffin batter into the prepared muffin cups, filling each about ¾ full. Sprinkle the topping generously over each muffin.

Place the muffin tin in the preheated oven and bake for 18–22 minutes until golden brown.

Allow the muffins to cool in the pan for 10 minutes before transferring them to a wire rack.