Preheat your oven to 425°F (218°C). Line a 12-cup standard muffin tin with paper liners or grease them thoroughly with non-stick spray. Ensure your eggs, milk, and sour cream are at room temperature to prevent the melted butter from seizing up when mixed.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt. In a separate small bowl, toss the blueberries with one tablespoon of the flour mixture. This prevents the berries from sinking to the bottom of the muffins during baking.

In a medium bowl, whisk the melted butter and sugar together (if not already in the dry mix) or simply combine the melted butter, eggs, sour cream, milk, lemon zest, lemon juice, and vanilla extract. Whisk until the mixture is smooth and the eggs are fully incorporated.

Gently pour the wet ingredients into the dry ingredients. Use a spatula to fold the mixture together until just combined. Do not overmix; a few streaks of flour are fine. Fold in the floured blueberries carefully. Scoop the batter into the muffin tins, filling them all the way to the top. Sprinkle with coarse sugar if desired.

Place the muffins in the oven at 425°F for 5 minutes. Then, without opening the oven door, reduce the temperature to 375°F (190°C) and bake for another 15 to 18 minutes. The muffins are done when a toothpick inserted into the center comes out clean. Let them cool in the pan for 5 minutes before transferring them to a wire rack.