Preheat the oven to 400°F (205°C). Spray a 6-cup muffin pan with nonstick spray or line it with cupcake liners, then set it aside.
Add the granulated sugar to a large bowl and, using your fingers, rub the lemon zest into the sugar until it’s well combined, fragrant, and the sugar has a yellow hue to it.
Add the egg and whisk until the mixture has thickened and is light in color, about 2 to 3 minutes. Whisk in the sour cream, oil, and lemon juice until well combined and no lumps from the sour cream remain, about 1 to 2 minutes. Set aside.
Add 1 cup (125 grams) of flour, baking powder, baking soda, and salt and stir until the flour is *mostly* incorporated. Toss the blueberries in the remaining ¼ cup (30 grams) of flour and then dump all of it into the batter. Fold everything together gently until just combined.
Spoon the batter into the prepared muffin pan, filling each cup to the top; you’ll use 4½ tablespoons of batter per cup. Sprinkle the tops with granulated sugar, if desired.
Bake the muffins for 15 to 17 minutes, or until a toothpick inserted into the center comes out mostly clean. Allow the muffins to cool for 10 minutes in the pan before removing them to a wire rack to cool completely.