Using a large mixing bowl and a hand mixer, blend together the butter and sugar.
Once blended, add egg, vanilla, and bananas; mix together well.
Add the flour, baking powder, baking soda, and salt to the bowl and incorporate into the wet ingredients.
Gently fold in the blueberries, reserving 1/4 cup.
Line a muffin tin with paper or silicone liners and scoop equal amounts of the batter into the paper cups. Do not fill more than 3/4 full.
Top the batter with the 1/4 cup blueberries you set aside.
Bake at 375 degrees for 20 minutes.
Allow muffins to cool for 5 minutes before removing from muffin tin and placing on a cooling rack to complete the cooling process.
Notes
The glaze is completely optional! Whisk one cup of confectioner's sugar with a little bit of milk. Start with one tablespoon of milk and add a little more until you get the desired consistency, if needed.