Step 1: Preheat and Prepare
Preheat your oven to 425°F (220°C). This high initial temperature is the secret to achieving those gorgeous domed tops. Line a 12-cup muffin tin with paper liners or generously grease with non-stick cooking spray. Set aside.

Step 2: Prepare the Blueberries
In a small bowl, gently toss the blueberries with 1 tablespoon of flour. This coating helps prevent the berries from sinking to the bottom and also prevents excess bleeding from frozen berries. Set aside.

Step 3: Mix Dry Ingredients
In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until well combined and no lumps remain. This ensures even distribution of leavening agents throughout your muffins.

Step 4: Combine Wet Ingredients
In a separate large bowl, whisk together the melted butter, eggs, sour cream, milk, and vanilla extract until smooth and well combined. The mixture should be relatively smooth with no large lumps of sour cream remaining.

Step 5: Combine Wet and Dry
Pour the wet ingredients into the bowl with the dry ingredients. Using a rubber spatula or wooden spoon, gently fold the mixture together just until combined. The batter should be thick and slightly lumpy. Do not overmix. It’s okay if you see a few small streaks of flour remaining. Overmixing will result in tough, dense muffins.

Step 6: Add Blueberries
Gently fold in the flour-coated blueberries with just a few strokes. Again, be careful not to overmix. The batter will be quite thick, which is exactly what you want for tall, bakery-style muffins.

Step 7: Fill Muffin Cups
Using an ice cream scoop or large spoon, divide the batter evenly among the 12 muffin cups. Fill each cup all the way to the top or even slightly mounded for the tallest muffin tops. Sprinkle the top of each muffin generously with sparkling sugar if using.

Step 8: Bake
Place the muffin tin in the preheated 425°F (220°C) oven and immediately reduce the temperature to 375°F (190°C). Do not open the oven door. Bake for 18-22 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean or with just a few moist crumbs.

Step 9: Cool
Remove from the oven and let the muffins cool in the pan for 5 minutes. This allows them to set properly. Then transfer the muffins to a wire cooling rack to cool completely, or enjoy them warm.