In a large mixing bowl mix together your butter and brown sugar.
Beat in your eggs, one at a time.
Mix in the vanilla, bananas (mashed) and peanut butter. If you want a nut bread you can use crunchy peanut butter.
Sift together your flour, powder, soda and salt to create a uniformity and to prevent holes in your bread. Then mix together with rest of the ingredients.
Lastly stir in your milk until everything is fully blended and smooth.
Pour batter into loaf pan and bake for approximately 65 minutes or until center comes out clean. Cool before removing from loaf pan so that the bottom doesn't separate.
Notes
If you don't have the baking powder you can always leave it out but just know that your bread may not rise as well.