Preheat oven to 180 degrees C. Lightly grease 24 muffin cups.
In a bowl, cream together the butter, sugar and vanilla. Mix in banana and sour cream. Stir in the eggs. In a separate bowl, mix the flour, baking powder and bicarb soda. Mix dry ingredients into the banana mixture until evenly moist. Fold in chocolate chips. Transfer batter to the prepared muffin cups, filling each cup about 3/4 full.
Bake 25 minutes in the preheated oven or until a knife inserted in the centre of a muffin comes out clean.