Preheat oven to 375°F (190°C) and line or grease a muffin tin.
In a bowl, whisk together gluten-free flour, sugar, baking powder, and salt.
In a separate bowl, whisk eggs, milk, oil (or butter), and vanilla until smooth.
Pour wet ingredients into dry ingredients and mix gently until just combined.
Toss blueberries with optional flour and gently fold into the batter.
Divide batter evenly among muffin cups, filling about ¾ full.
Bake for 20–24 minutes, until tops are lightly golden and a toothpick comes out clean.
Cool in the pan for 5 minutes, then transfer to a wire rack.