Best Blueberry Muffins (TO DIE FOR)

NOTE: I use frozen blueberries and half whole milk yogurt and half whole milk. If you prep the ingredients the night before this is a really quick breakfast.

Makes 12 muffins
If buttermilk is unavailable, substitute 3/4 cup plain whole-milk or low-fat yogurt thinned with 1/4 cup milk.

INGREDIENTS
Lemon-Sugar Topping
1/3cup sugar (2 1/3 ounces)
1 1/2teaspoons finely grated zest from 1 lemon

Muffins
2cups fresh blueberries (about 10 ounces), picked over
1 1/8cups sugar (8 ounces) plus 1 teaspoon
2 1/2cups unbleached all-purpose flour (12 1/2 ounces)
2 1/2teaspoons baking powder
1teaspoon table salt
2large eggs
4tablespoons (1/2 stick) unsalted butter , melted and cooled slightly
1/4cup vegetable oil
1cup buttermilk (see note)
1 1/2teaspoons vanilla extract

INSTRUCTIONS
1. FOR THE TOPPING: Stir together sugar and lemon zest in small bowl until combined; set aside.
2. FOR THE MUFFINS: Adjust oven rack to upper-middle position and heat oven to 425 degrees. Spray standard muffin tin with nonstick cooking spray. Bring 1 cup blueberries and 1 teaspoon sugar to simmer in small saucepan over medium heat. Cook, mashing berries with spoon several times and stirring frequently, until berries have broken down and mixture is thickened and reduced to ¼ cup, about 6 minutes. Transfer to small bowl and cool to room temperature, 10 to 15 minutes.
3. Whisk flour, baking powder, and salt together in large bowl. Whisk remaining 11/8 cups sugar and eggs together in medium bowl until thick and homogeneous, about 45 seconds. Slowly whisk in butter and oil until combined. Whisk in buttermilk and vanilla until combined. Using rubber spatula, fold egg mixture and remaining cup blueberries into flour mixture until just moistened. (Batter will be very lumpy with few spots of dry flour; do not overmix.)
4. Following photos below, use ice cream scoop or large spoon to divide batter equally among prepared muffin cups (batter should completely fill cups and mound slightly). Spoon teaspoon of cooked berry mixture into center of each mound of batter. Using chopstick or skewer, gently swirl berry filling into batter using figure-eight motion. Sprinkle lemon sugar evenly over muffins.
5. Bake until muffin tops are golden and just firm, 17 to 19 minutes, rotating muffin tin from front to back halfway through baking time. Cool muffins in muffin tin for 5 minutes, then transfer to wire rack and cool 5 minutes before serving.

TECHNIQUE
WHEN MORE ISN'T BETTER
To boost berry flavor in a muffin, simply adding more blueberries isn't the answer. With too many in the mix, the berries sink to the bottom, weighing the muffin down.