Preheat the oven to 425°F and line 6 muffin cups or lightly spray with nonstick spray.
In a medium bowl, whisk together the flour, baking powder, and sea salt.
In a separate bowl, whisk together the melted and cooled butter abd sugar until smooth and glossy.
Add the egg, milk, lemon juice, lemon zest, vanilla extract, and Greek yogurt (or sour cream) and whisk until combined and creamy.
Add the dry ingredients to the wet ingredients and stir gently just until partially combined.
Fold in the blueberries with a rubber spatula, finishing the mixing as you go. Be careful not to over-mix the batter.
Use a 4 tablespoon cookie scoop to scoop the batter into 6 muffin cups. You may have some batter leftover for a smaller muffin, but doint overfill the 6 cups.
Sprinkle the tops lightly with sugar, if desired.
Bake for muffins for 5 minutes at 425˚, then reduce to 375˚ and bake for 13-15 mintues. rotating the pan halfway through baking, until the tops are lightly golden and a toothpick inserted into the center comes out mostly clean.
Let the muffins cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
Store muffins in an airtight container for 3–5 days or freeze for up to 3 months.
Notes
Don’t over-mix the batter. Muffin batter should look slightly lumpy when you stop mixing.
Don't overfill the muffin cups, 4 tablespoons is the perfect amount.
If your Greek yogurt is very thick, the batter may seem a little thicker than expected. That’s okay.
The sugar on top gives these a lightly crisp bakery-style top that I highly recommend.
Bake at 425˚ for the first 5 minutes, then reduce to 375˚ degrees for the remainder of the baking time.
Keep an eye on them towards the end of baking, so they don't get too done. They lose their fluffy texture when they're over-baked.
These muffins freeze really well. Store them in an airtight container in the freezer for up to 3 months.