Preheat the oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease it lightly.
In a large mixing bowl, whisk together 2 cups all-purpose flour, granulated sugar, baking powder, baking soda, and salt until well combined.
In a separate bowl, whisk together the melted butter, buttermilk, eggs, and vanilla extract until smooth.
Toss the frozen blueberries with 2 tablespoons of flour to coat them evenly. This helps prevent the berries from sinking to the bottom of the muffins.
Pour the wet ingredients into the dry ingredients and gently fold together until just combined. Do not overmix; the batter should be slightly lumpy.
Carefully fold in the coated frozen blueberries, distributing them evenly throughout the batter.
Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full.
Bake in the preheated oven for 18 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and allow them to cool in the pan for 5 minutes.
Transfer the muffins to a wire rack to cool completely before serving.