Preheat the oven to 350˚F (180˚C)
In a stand mixer, cream butter until fluffy.
Add sugar to butter and beat.
Add eggs, one at a time, and beat until well mixed.
Add vanilla and mashed banana and beat gently.
In a medium-sized bowl, stir together flour, baking powder, baking soda, and salt.
Beat dry mixture into banana mixture alternately with buttermilk.
Gently mix in the chocolate chips.
Line a standard muffin tin with paper muffin liners.
Pour the batter into the lined muffin tin, distibuting evenly.
Bake for 20 minutes, checking at about 18 minutes with a tootpick for doneness.