In small sauce pan, cook butter on medium heat. Allow butter to simmer, stirring often, until it turns a darker golden color. Dark bits may form on bottom of pan, which is fine. Pour into large mixing bowl and let cool for 5 minutes.
Preheat oven to 350°. Line 2 muffin pans with cupcake liners.
To large bowl with butter, add banana, sugar, eggs, and vanilla. Combine well.
Meanwhile, in small bowl, mix flour, baking soda, and salt. Add dry mixture to banana mixture. Stir to combine, do not over-mix.
Gently fold in blueberries. Evenly divide batter among 24 liners and bake for 23 - 25 minutes.
Cool for 5 minutes in pans, then remove muffins to wire rack to finish cooling. Enjoy!
Notes
For optional drizzle on top, mix 3/4 cup powdered sugar with 2 - 3 tablespoons heavy cream.