Add bananas to a large mixing bowl and mash with a fork. Stir in vanilla and egg until completely combined.
Next, stir in the canola oil and milk. Add the brown sugar and white sugar and stir well.
To the bowl, add the salt, baking soda, all-purpose flour, and cocoa powder. Gently fold the dry ingredients into the wet mixture until combined — do not over mix at this point.
Divide the batter among 12 paper-lined muffin cups. Sprinkle the chocolate chips on top and bake for 5 minutes at 425 degrees.
Reduce the oven temperature to 375 degrees (without opening the oven door) and continue baking for another 8 to 10 minutes, or until a pick inserted into the center of the muffins comes out clean.
Let cool in the muffin tin for 5 minutes before removing to a wire rack to cool completely.
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Notes
Recipe adapted from Fork Knife Swoon.Serve muffins warm or at room temperature.Muffins will stay moist for 3-4 days stored in a ziplock bag or sealed container.