- Preheat oven to 350°F. Prepare batter: In a large bowl, mix flour, baking powder, and baking soda. In a small bowl, whisk 1 egg with oil; stir in 1⁄2 cup yogurt, maple syrup and vanilla. Add egg mixture to flour mixture and stir until just combined. Mash 2 1⁄2 bananas and fold into mixture until just combined and no white streaks remain; mixture should still be lumpy.
- Meanwhile, prepare filling: In a small bowl, mash remaining 1⁄2 banana Stir in remaining 1 egg, 2 tablespoon yogurt and peanut butter until well combined. Line 14 muffin cups with paper liners and fill one-third of each liner with batter.
- Dollop 1 teaspoon filling into each, then divide remaining batter among liners. Bake for 18 to 25 minutes, until a toothpick comes out clean when inserted in center. Let cool in tin for 5 minutes, then remove muffins from tin and let cool on wire racks.