Preheat the oven to 400?F (204?C). Line muffin cups with paper liners (8 for big muffins, 10 for standard, or 22 for mini). Lightly grease or spray the tops of the muffin tin with oil.

Use a microplane or citrus zester to remove the zest from the lemon. Add the zest to a small bowl with the sugar. Rub the zest into the sugar until the lemon perfumes it.

Whisk the flour, lemon sugar, baking powder, and salt in a large bowl.

Add the oil to a measuring jug, then crack in the egg. Pour in enough milk to reach the 1-cup line. Add the vanilla extract and whisk until combined.

Add the wet ingredients to the bowl with the dry ingredients and stir gently until the batter comes together.

Gently fold in the blueberries and about 2 tablespoons of fresh lemon juice.

Divide the batter between muffin cups. Sprinkle a little sugar on top of each muffin and add a very thin slice of lemon if desired.

Bake muffins for 15 to 20 minutes or until the tops are no longer wet and a toothpick inserted comes out with crumbs. Transfer to a cooling rack.