Preheat oven to 350 degrees. Grease a loaf pan with nonstick cooking spray.
In a large bowl, beat the butter, vanilla and sugar until light and fluffy. Beat in the eggs.
In a separate bowl, mash the bananas and milk together.
In a third bowl, whisk together the flour, salt and baking soda. Blend dry ingredients into the creamed mixture alternately with the bananas. Pour half of the batter into the prepared loaf pan.
Place chocolate chips into a microwave safe dish and melt for 30 seconds on high power in the microwave. Add the peanut butter and melt for another 30 seconds. Stir together until smooth. Pour half of the mixture evenly over the bread batter. Top with the remaining batter and peanut butter mixture.
Bake for 60-70 minutes, until a cake tester comes out clean. Allow to cool completely before turning it out of the pan.