Let the melted butter cool a bit before adding it to the sugar and egg mixture. You don’t want the heat from the butter to scramble the egg.
Be sure to use ripe bananas for these muffins. Under ripe bananas don’t add enough sweetness and overripe bananas can make the muffins gooey.
When adding the dry ingredients to the wet ingredients, be careful to not overmix the batter. Overmixing can lead to muffins that are tough.
Use a large scoop to fill the muffin cups with batter. This will keep the muffins similar in size and ensure even baking time.
Remove the muffins from the pan to finish cooling on a wire rack. If you leave the muffins in the pan to cool, the bottoms of the muffins may become soggy.