Blueberry Muffins – Makes 12 Muffins

Lemon-Sugar Topping
1/3 cup ( 2 1/3 ounces) sugar
1 ½ tsp finely grated zest from 1 lemon
2 cups ( about 10 ounces) fresh blueberries
1 teaspoon plus 1 1/8 cups (8 ounces sugar)
2 ½ cups ( 12 ½ ounces ) unbleached all- purpose flour
2 ½ teaspoons baking powder
1 teaspoon table salt
2 large eggs
4 tablespoons (1/2 stick ) unsalted butter, melted & cooled slightly
4 tablespoons vegetable oil
1 cup buttermilk
1 ½ teaspoons vanilla extract

For the Topping: Stir the sugar and lemon zest together in a small bowl until combined and set aside.

For the Muffins: Adjust an oven rack to the upper middle position and heat the oven to 425 degrees. Spray a standard- size muffin pan with vegetable oil spray. Bring 1 cup of the blueberries and 1 teaspoon of the sugar to a simmer in a small saucepan over medium heat. Cook, mashing the berries with a spoon several times and stirring frequently, until the berries have broken down and the mixture is thickened and reduced to ¼ cup, about 6 minutes. Transfer to a small bowl and cool to room temperature, 10 to 15 minutes.
Whisk the flour, baking powder, and salt together in a large bowl. Whisk the remaining 1 1/8 cups sugar and the eggs together in a medium bowl until thick and homogeneous, about 45 seconds. Slowly whisk in the butter and oil until combined. Whisk in the buttermilk and vanilla until combined. Using a rubber spatula, fold the egg mixture and remaining 1 cup blueberries into the flour mixture until just moistened. (The batter will be very lumpy with a few spots of dry flour: do not over mix).
Using a 1/3 cup measure or an ice cream scoop, divide the batter equally among the prepared muffin cups ( the batter should completely fill the cups and mound slightly). Spoon 1 teaspoon of the cooked berry mixture into the center of each mound of batter. Using a chopstick or skewer, gently swirl the berry filling into the batter using a figure-eight motion. Sprinkle the lemon sugar evenly over the muffins.
Bake until the muffin tops are golden and just firm, 17 to 19 minutes. Rotating the pan halfway through baking. Cool the muffins in the pan for 5 minutes, then transfer them to a wire rack and cool for 5 minutes before serving.