Preheat your oven to 350 degrees. Grease a standard muffin tin or fill with cupcake liners and set aside.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, salt, cinnamon, and nutmeg.
In a medium bowl, mix together the Greek yogurt, eggs, melted butter, 1 teaspoon vanilla extract, and mashed bananas.
Make a well in the flour mixture. Pour in the banana mixture and fold until just combined. Mix in the blueberries.
Fill each muffin cup until completely full (not 3/4 full or you won't get a good muffin top).
Place in the oven with a cookie sheet underneath to catch any drips.
Bake for 40 minutes, or until a toothpick inserted in the center of a muffin comes out clean.
Allow the muffins to fully cool.
To make the glaze: whisk together the powdered sugar, milk, and remaining 1 teaspoon vanilla extract until a glaze is formed. Add additional milk, if needed.
Refrigerate the vanilla glaze until ready to use and remix prior to glazing the muffins.
Drizzle the glaze over each muffin and enjoy. Refrigerate leftover banana blueberry muffins with vanilla glaze.