Preheat my oven to 350℉. Then, I lightly grease 15 muffin cups or line them with paper liners. This ensures the muffins don't stick.
In a small bowl, I whisk together the gluten-free flour blend, baking powder, and salt. I set this aside for a moment.
In a large bowl, I combine the softened butter and granulated sugar. I beat them on medium-low speed until the mixture becomes thick and creamy.
With the mixer still running, I add the eggs one at a time, beating until they are fully combined with the butter mixture.
I add the dry ingredients to the wet mixture and mix on low speed until it thickens. Then, I stop the mixer, add the milk and vanilla extract, and mix again until a thick batter forms. Be careful not to overmix!
Now, I gently fold in the blueberries with a rubber spatula. If I'm using frozen or cold blueberries, the batter will get VERY thick, which is totally normal.
I spoon the batter into the prepared muffin pans, filling each cavity about ⅔ full. If I'm feeling fancy, I'll top each muffin with about 1 teaspoon of granulated sugar for a lovely crunchy finish. This sugar topping is completely optional, though!
I bake the muffins for about 25 minutes, or until a cake tester inserted into the center of one of the muffins comes out clean. This tells me they're perfectly baked through.
I allow the muffins to cool in the pan for five minutes, then I transfer them to a wire rack to cool completely. Once cooled, I store them covered on the counter where they’ll keep for about three days. They also freeze beautifully! I place the cooled muffins in a freezer bag and freeze them for up to two months. When I'm ready to enjoy one, I simply allow the muffin to thaw at room temperature.