Preheat your oven to 375°F (190°C) and prepare your muffin tin by lining it with muffin liners or greasing it lightly.
In a large mixing bowl, whisk together the gluten-free flour, granulated sugar, baking powder, and salt until well combined.
In another bowl, beat the eggs and then add the melted butter, milk, and vanilla extract. Whisk until smooth and fully incorporated.
Pour the wet ingredients into the dry mixture and stir until just combined. Be careful not to overmix; a few lumps are perfectly fine.
In a small bowl, toss the blueberries with the 1/4 cup of gluten-free flour. This helps prevent them from sinking to the bottom of the muffins.
Gently fold the floured blueberries into the muffin batter until evenly distributed.
In a separate small bowl, mix the brown sugar, granulated sugar, ground cinnamon, and salt. Cut in the cold butter until the mixture resembles coarse crumbs.
Spoon the muffin batter evenly into the prepared muffin cups, filling them about 3/4 full. Sprinkle the topping mixture generously over each muffin.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for about 5 minutes, then transfer them to a wire rack to cool completely. Enjoy warm or at room temperature!