Preheat oven to 180 C (355 F) and line a mini muffin tray with paper muffin cups.
Sift flour into a mixing bowl.
Whisk egg and milk together, then add to flour and mix well.
Mash banana and peanut butter in a small bowl until smooth and blended together.
Add to mixing bowl and combine well.
Fill mini muffin cups 3/4 full.
Bake for approx 20 mins, or until toothpick inserted into them comes out clean.