In a large bowl, mix together your melted butter, sugar, eggs and vanilla
In a separate bowl combine the flour, baking soda and salt
Stir flour mixture into the large bowl containing the butter mixture
Stir in the yogurt and mashed bananas – mix until well incorporated
Spread into your greased bread loaf pan
Spoon 3 lines of your peanut butter the full length (horizontal) of your baking pan on top of your banana bread batter. Next, run a knife up and down (verticle) through your peanut butter lines to create a swirl effect.
Bake at 350 degrees for 60 minutes, or until a knife or toothpick inserted into the center of the loaf comes out clean.
Cool bread in the pan for 10 – 15 minutes prior to removing. Finish cooling on a wire rack.