Place muffin liners into muffin pan
Preheat oven to 350 degrees
In mixer bowl cream butter with brown sugar
Mix in egg, banana, and heavy cream until combined
Add in flour, baking powder, baking soda and salt and mix on low until all incorporated
On medium-low add in oatmeal and nuts
Place 3 tablespoons of batter into each muffin liner
sprinkle each muffin with brown sugar and oatmeal
Bake for 30 minutes or until a toothpick comes out almost just tacky. If you bake them until the toothpick is dry the muffins will be dry. (I set a timer for 25 minutes and test every minute, just in case the oven is hot)