1/4 cup butter, margarine or shortening
1/2 cup sugar
1/4 cup sour milk (put a little lemon juice or vinegar - 1 tsp is enough - in
your measuring cup and fill to 1/4 cup with regular milk; let sit a few
minutes to sour)
1 egg
1/2 cup banana (I find 1 banana is about right)
1/2 teaspoon soda
1 teaspoon baking powder
1 cup flour
dissolved in milk. Add dry ingredients, then mashed banana. 
Options: add  chopped nuts and/or chocolate chips as desired.
NOTE: I usually double or triple this recipe to make a 9x12" pan . If you
only use basic recipe, a loaf pan or a 8x8" pan might be about right. If
making muffins, fill greased or paper lined cups about 2/3's full.

BAKE AT 350 degrees F.
Times:
Double or triple recipe 9x12" pan: 25-30 mins.
8x8" single recipe 20-25 mins.
Muffins: 10-15 mins.

Test with toothpick - should come out clean when done.