Preheat and prep: Heat your oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease lightly. This higher temperature helps create tall, rounded tops.
Mix the dry ingredients: In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt until well combined. Even mixing here means even rise later.
Whisk the wet ingredients: In a separate bowl, whisk melted butter, oil, buttermilk, eggs, vanilla, and lemon zest until smooth. Make sure the butter is cooled so it doesn’t scramble the eggs.
Toss the berries: In a small bowl, toss the blueberries with 1 tablespoon of flour. This light coating helps keep them suspended in the batter.
Combine gently: Pour the wet ingredients into the dry. Stir with a spatula just until a few flour streaks remain. Fold in the blueberries with 2–3 gentle strokes. Do not overmix; a lumpy batter is perfect.
Fill the tin: Divide the batter evenly among the cups, filling them to the top. Sprinkle with coarse sugar for a crisp, bakery-style lid.
Bake for lift: Bake at 400°F (200°C) for 8 minutes, then reduce heat to 350°F (175°C) without opening the door. Continue baking 10–13 minutes, or until the tops are golden and a toothpick comes out with a few moist crumbs.
Cool smartly: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack. This prevents soggy bottoms and keeps the crumb tender.
