Heat oven to 350°F (175°C) and grease or line your muffin tin.
In a bowl, combine chopped pecans, brown sugar, and flour. Stir until blended.
In another bowl, whisk eggs, then add melted butter.
Pour wet ingredients into dry ingredients and stir just until combined. Do not overmix.
Spoon batter into muffin tin, filling each about ⅔ full. Batter will be thick.
Bake for 20–25 minutes until golden brown and a toothpick inserted in the center comes out clean.
Allow muffins to cool in the pan for 10 minutes, then transfer to a wire rack. Serve warm or at room temperature.