
Heat the oven to 375ºF.
Cream butter with lemon zest and 1 cup of the sugar until light and fluffy.
Add the egg and vanilla and beat until combined. Meanwhile, toss the blueberries with ¼ cup of flour; then whisk together the remaining flour, baking powder, and salt.
Add the flour mixture to the batter a little at a time, alternating with the milk. Fold in the blueberries.
Grease the muffin tin and distribute batter among muffin cups. Sprinkle remaining tablespoon of sugar on top.
Bake for 30 minutes (or 18-25 minutes for a 12-cup muffin tin). Check with a toothpick for doneness.
Let muffins cool in pan for about 7 minutes before serving.