Preheat the oven to 350°F. Line a 12-cup muffin pan with muffin liners. Set aside.
Peel bananas and add to a large mixing bowl. Using a pastry cutter (recommended), sturdy whisk or fork, mash bananas until smooth. Add the coconut oil, maple syrup, flax egg and vanilla. Whisk until well incorporated.
Add dry ingredients to wet ingredients. Whisk together as long as you can. Switch to stirring and folding with a rubber spatula until well incorporated and no flour patches remain. Fold in chocolate chips. Batter will be very thick—do not add additional liquids.
Using a large scoop, scoop and drop batter evenly into prepared muffin pan. Fill each cup all the way to the top for a smaller quantity of big, round-topped muffins, and ¾ of the way for a larger quantity of smaller muffins. Optionally, sprinkle with chocolate chips and lightly press down into each muffin top.
Bake for 18-28 minutes. Mine took 23 minutes for large, high-topped muffins. Place muffin pan onto a cooling rack for 30 minutes. Then, gently transfer muffins directly onto cooling rack for 1 hour to cool completely. Enjoy! Storing instructions below.
Storing Instructions: Store in an airtight container for up to 1 week.Freezing Instructions: These muffins freeze well. Store in an airtight container in the freezer for up to 1 month. Allow to thaw at room temperature for 30 minutes, or heat in the microwave in 10-second increments until just warm.