Spray a muffin tin with nonstick cooking spray or line with paper or silicone liners, set aside. Preheat oven to 350 °F.
In a bowl, combine the chopped pecans, flour, baking powder, salt, vanilla extract and brown sugar. Add the eggs and butter. Stir until mixed well.
Spoon into muffin tin to fill each cup.
Bake 20 to 25 minutes, or until a toothpick inserted in the middle of the muffins comes out clean. Remove from oven. Cool in pan a few minutes, then remove to cooling rack to cool completely.