1 1/4 cups (175 g) all purpose gluten free flour (I used Better Batter)
3/4 teaspoon xanthan gum (omit if your blend already contains it)
2 tablespoons (18 g) cornstarch
1/2 teaspoon baking powder
1/8 teaspoon baking soda
1/4 teaspoon kosher salt
1/2 cup (100 g) granulated sugar
3/4 cup (about 125 g) whole blueberries (fresh or frozen)*
8 tablespoons (112 g) unsalted butter, melted and cooled
1 egg (50 g, weighed out of shell) at room temperature, beaten
1 teaspoon pure vanilla extract
3 tablespoons (1 1/2 fluid ounces) buttermilk, at room temperature
Coarse sugar, for sprinkling (optional)
*If your blueberries are frozen, do not defrost them before adding them to the muffin top batter. Just rinse them in cold water before tossing in the dry ingredients as described in the recipe instructions below.
Preheat your oven to 375°F. Line a large rimmed baking sheet with unbleached parchment paper and set it aside.
In a large bowl, place the flour, xanthan gum, cornstarch, baking powder, baking soda, salt, and granulated sugar, and whisk to combine well. Transfer 1 tablespoon of the dry ingredients to a small bowl, add the blueberries and toss to coat, then set the blueberries aside. Create a well in the center of the dry ingredients and add the butter, egg, vanilla, and buttermilk, and mix until just combined. Add the blueberries and reserved dry ingredients, and gently fold the berries into the batter just until they are evenly distributed throughout.
Scoop the dough into about 7 mounds, each about 3 tablespoons, and place about 1 1/2-inches apart from one another. With wet hands, press each mound down lightly to form a thick disk. Sprinkle each top lightly with coarse sugar.
Place the baking sheet in the center of the preheated oven and bake until puffed and set in the center, and just beginning to brown on the edges (about 14 minutes). Remove the baking sheet from the oven and allow the muffin tops to cool for 10 minutes before transferring to a wire rack to cool completely.