Prep the pan: Heat the oven to 425°F (220°C). Grease a jumbo muffin tin or line with jumbo paper liners. This recipe makes 6 jumbo muffins.

Mix the dry ingredients: In a large bowl, whisk 2 1/2 cups all-purpose flour, 3/4 cup granulated sugar, 1/4 cup light brown sugar, 1 tablespoon baking powder, 1/2 teaspoon baking soda, 1/2 teaspoon kosher salt, and a pinch of cinnamon.

Whisk the wet ingredients: In a separate bowl, whisk 1 cup buttermilk, 1/3 cup neutral oil, 1/4 cup melted unsalted butter (cooled), 2 large eggs, 2 teaspoons vanilla, and the zest of 1 lemon if using.

Prep the berries: Toss 2 cups blueberries with 1 tablespoon flour to lightly coat. This helps keep them from sinking.

Combine gently: Pour the wet ingredients into the dry. Fold with a spatula just until the flour streaks are almost gone. Add the blueberries and fold a few more times. Stop while it’s still lumpy. Overmixing makes tough muffins.

Fill the cups: Divide the batter evenly among the 6 muffin cups, filling nearly to the top. Sprinkle generously with coarse sugar.

Bake high, then lower: Bake at 425°F for 7–8 minutes. Without opening the oven, reduce the temperature to 350°F (175°C) and continue baking 15–18 minutes, until the tops are golden and a toothpick comes out with a few moist crumbs.

Cool briefly: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack. Serve warm or at room temperature.