In a large bowl or bowl of a stand mixer, cream together butter and brown sugar. Add bananas and mix, then mix in eggs.
8 tablespoons butter, 1 cup brown sugar, 2 eggs, 4 bananas
Gradually add dry ingredients to banana mixture, mixing just until fully incorporated and no dry bits remain.
Divide batter among muffin cups. Bake for 18-20 minutes, until golden and a toothpick inserted in the center only has moist crumbs. Let cool in the pan a few minutes before removing to a wire rack to cool completely.