Preheat the oven to 350°F. In a large bowl, cream together the softened butter and brown sugar with an electric handheld mixer. Add the eggs, vanilla extract, and mashed banana and beat until creamy.

In a separate bowl, whisk together the flour, baking soda, and salt. Add to the combined wet ingredients and mix at low speed just until combined. Fold in the butterscotch chips and chopped pecans.

Spoon batter into muffin tins lined with parchment liners ¾ full. Top with additional pecans, if desired. Bake in the preheated oven for 20-25 minutes or until a toothpick inserted into the center comes out clean. Top with additional butterscotch chips right after baking.