Mix melted butter and brown sugar until smooth.
Whisk in egg and vanilla extract until fully blended.
Stir in flour and salt until just combined.
Fold in chopped pecans evenly through the batter.
Spoon batter into greased muffin tin, ¾ full.
Top with whole pecans if desired.
Bake at 350°F for 15–18 minutes, until centers are soft and edges golden.
Cool in pan for 10 minutes before removing.
