Preheat oven to 350 degrees F. Grease a 9-inch loaf pan.
In a medium mixing bowl, mix flour, baking powder, baking soda and salt together and set aside.
In a large mixing bowl, beat butter, sugar, and mashed banana together until very creamy about 2 minutes. Add vanilla and eggs and beat until well combined. Add in yogurt, and milk and mix until just combined.
Add dry ingredients to wet ingredients. Mix until well combined. Gently fold in 1 ¼ cup of chopped peanut butter cups.
Pour batter into loaf pan. Sprinkle 1/3 cup of chopped peanut butter cups over the top. Bake for 55-65 minutes, or until golden brown and toothpick comes out almost clean in center.
Cool for 10 minutes in pan, then remove from pan gently and transfer to wire rack. Cool completely.
This bread is even better the next day.
Makes 12 slices, depending on how thick you like them.