Preheat the oven to 425°F. Line a muffin tin with liners,
In a large bowl, mashed your bananas.
Add in the oil, milk, egg, and vanilla. Beat well.
Add in the sugar and peanut butter, beat well.
In a medium bowl, stir together the four, salt, and baking soda.
Pour the dry ingredients into the wet and stir until just combined, there will be lumps, and that is okay.
Evenly divide the batter in the muffin tin, and bake for 5 minutes. Turn down the heat to 350°F without opening the oven door, and continue to bake for 12 - 15 minutes, or until a toothpick inserted in the middle of a muffin comes out clean.
Use creamy peanut butter. Natural peanut butter can work, as long as you stir the peanut butter well first.