Preheat your oven to 350°F (175°C). Generously grease the mini or regular muffin tins to prevent sticking.
In a medium-sized mixing bowl, combine the brown sugar, flour, and chopped pecans.
In a separate bowl, whisk together the softened butter and beaten eggs until well blended. Add the dry ingredients and gently stir until just incorporated.
Fill the prepared muffin cups about two-thirds full with the batter.
Bake in the preheated oven for 12 to 13 minutes for mini muffins or 15 to 17 minutes for regular-sized muffins.
Once baked, carefully run a knife around the edge of each muffin to release them from the pan.