Prep your pan: Heat oven to 425°F (220°C).Line a jumbo muffin pan (6-cup) with paper liners or grease well. For standard-size muffins, use a 12-cup pan. Mix dry ingredients: In a large bowl, whisk 2 3/4 cups all-purpose flour, 1 cup granulated sugar, 1/4 cup brown sugar, 1 tablespoon baking powder, 1/2 teaspoon baking soda, and 1/2 teaspoon kosher salt. Set aside 1 tablespoon of this mixture to toss with the blueberries.
Combine wet ingredients: In a medium bowl, whisk 1/2 cup melted unsalted butter (slightly cooled), 1/4 cup neutral oil, 2 large eggs, 3/4 cup sour cream (or Greek yogurt), 1/2 cup milk, and 2 teaspoons vanilla extract.Add 1–2 teaspoons lemon zest if using. Bring batter together: Pour wet ingredients into dry. Stir with a spatula just until a few dry streaks remain. The batter should be thick; avoid overmixing.
Prepare blueberries: Toss 1 3/4 to 2 cups blueberries with the reserved flour mixture.Gently fold into the batter. If using frozen berries, fold straight from the freezer to minimize streaking. Fill the cups fully: Divide batter evenly among the jumbo cups, filling to the top. A heaping scoop encourages a high dome.Sprinkle generously with coarse sugar. Bake high, then lower: Bake at 425°F (220°C) for 8 minutes to jump-start the rise. Without opening the oven, reduce heat to 350°F (175°C) and bake 16–20 more minutes, until tops are golden and a toothpick comes out with just a few moist crumbs.
Cool smartly: Let muffins cool in the pan for 5 minutes, then transfer to a rack. This prevents soggy bottoms while keeping interiors moist.
Serve: Enjoy warm or at room temperature.The tops will be slightly crisp with a fluffy, tender center.
