2½tspbaking powder(If you don't have it on hand, you can make it with baking soda, cream of tartar and arrowroot flour or non-GMO cornstarch. Here's how.)
Preheat your oven to 350 degrees and place 10-12 parchment paper liners into the muffin tin. (The coconut flour version makes 10-11, and the oat flour version makes 11-12.)
Mash the bananas with a fork and measure out 1½ cups.
Add all the wet ingredients (mashed bananas, eggs, maple syrup and butter/coconut oil) to a high-speed blender or food processor and blend until smooth.
Add all dry ingredients except the pecans/walnutson top of the wet ingredients and blend again until smooth.
Stir in 1/4 cup of the nuts. You can transfer the mixture to a bowl for this step if you'd like. Personally, I just remove my blender container from the base, add the nuts, and then use a silicone spatula to mix them in. (That's one less bowl to wash!)
Place about 1/3 cup batter into each cup, then sprinkle the remaining 1/2 cup of the nuts over the top of the muffins.
Bake for 25-30 minutes, or until a toothpick comes out clean. Store any leftovers in an airtight container.
Notes
Nutrition values are estimated based on the use of butter, coconut flour and pecans in the recipe (instead of coconut oil, oat flour and walnuts).