Preheat oven to 400°.
Sift the flour into a mixing bowl and add baking powder, salt, and sugar.
In a small bowl, crack the egg and beat with a wire whisk or fork for 10 seconds. Add milk and oil to the egg and stir to blend.
Make a well in the flour and pour in the egg-milk mixture. Stir as little as possible to moisten the flour. Set the batter aside for a moment while mixing the blueberries with the lemon zest. Fold the berry mix into the muffin mix, again stir gently and as little as possible. Spoon batter into the tins to three-fourths full.
Put muffins in 400° oven and set timer for 20 minutes. It may take them an additional 5 minutes to become golden brown. Check at 15 minutes and if they are browning too quickly, place on bottom shelf or cover with a length of aluminum foil or brown paper.
When the muffins are baked, cool for 5 minutes. Run a knife around the edges of each. Tilt the tray and gently lift each muffin from its tin.
Dip the top of each lightly in the melted butter and then in the sugar.
The muffins can be held overnight and heated for eating the following day. They can also be frozen, but fresh-baked are best.
Makes 9-12 muffins.