In a large bowl, stir together flours, baking powder, baking soda and salt.
In another bowl cream butter and sugar until light and fluffy; beat in eggs. Stir in banana, milk and vanilla.
Add dry ingredients and stir just to combine; stir in walnuts or mini chocolate chips.
Spoon batter into greased or paper lined muffin cups until 2/3 full.
Bake at 375 degrees for 20-25 minutes.
Cool 5 minutes before removing from pan; finish cooling on wire rack.