Prep the pan: Heat the oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or lightly grease each cup.
Mix the dry base: In a large bowl, whisk the flour, sugar, baking powder, baking soda, and salt until well combined and no streaks remain.
Add the wet ingredients: Make a well in the center. Add the oil, eggs, buttermilk, and vanilla (and lemon zest if using). Whisk the wet ingredients together in the well, then fold into the dry until just combined. The batter should be thick and a little lumpy.
Toss the berries: In a small bowl, toss the blueberries with 1 tablespoon flour. This helps prevent sinking and streaking. Gently fold the berries into the batter using a spatula.
Fill the cups: Divide the batter evenly among the muffin cups, filling them almost to the top for taller domes. Sprinkle with coarse sugar if you like a crunchy lid.
Bake hot, then finish: Bake at 400°F (200°C) for 5 minutes to jump-start the rise. Without opening the oven, reduce the temperature to 350°F (175°C) and bake 12–15 minutes more, until the tops are golden and a toothpick comes out with a few moist crumbs.
Cool and enjoy: Let the muffins cool in the pan for 5 minutes, then transfer to a rack. They’re great warm, but even better once the crumb sets after about 20 minutes.
