Best Blueberry Muffins with Streusel Topping

Ingredients

• 3 tablespoons granulated sugar
• 3 tablespoons dark brown sugar
• Pinch salt
• 1/2 cup plus 3 tablespoons (3-1/2 ounces)all-purpose flour
• 5 tablespoons unsalted butter melted
• 2 cups(abt. 10 ounces) fresh blueberries picked over
• 1-1/8 cups plus 1 teaspoon granulated sugar divided
• 2-1/2 cups all-purpose flour
• 2-1/2 teaspoons baking powder
• 1 teaspoon salt
• 2 large Eggs
• 4 tablespoons (1/2 stick) unsalted butter melted and cooled slightly
• 1/4 cup vegetable oil
• 1 cup buttermilk (See note)
• 1-1/2 teaspoons vanilla extract

Instructions

1. To prepare streusel topping, combine 3 tablespoons granulated sugar, dark brown sugar, pinch salt and 1/2 cup plus 3 tablespoons flour in a small bowl. Drizzle with 5 tablespoons warm, melted unsalted butter and toss with a fork until evenly moistened and mixture forms large chunks with some pea-sized pieces throughout. Set aside.
2. Adjust oven rack to upper-middle position and heat oven to 425F. Using standard muffin tins, line or spray with nonstick cooking spray. Set aside.
3. In a small saucepan, bring 1 cup blueberries and 1 teaspoon granulated sugar to a simmer over medium heat. Cook, mashing berries with a spoon several times and stirring frequently, until berries have broken down and mixture is thickened and reduced to 1/4 cup, about 6 minutes. Transfer to a small bowl and cool to room temperature, 10 to 15 minutes.
4. In a large bowl, whisk together flour, baking powder and salt. In a medium bowl, whisk remaining 1-1/8 cups granulated sugar and eggs together until thick and homogeneous, about 45 seconds. Slowly whisk in melted butter and oil until combined. Whisk in buttermilk and vanilla until combined. Using a rubber spatula, fold egg mixture and remaining 1 cup blueberries into flour mixture until just moistened. (Batter will be very lumpy with a few spots of dry flour; do not overmix.)
5. Using an ice cream scoop or large spoon, divide batter equally among prepared muffin cups (batter should completely fill cups and mound slightly). Spoon 1 teaspoon of cooked berry mixture into the center of each mound of batter. Using a chopstick or skewer, gently swirl berry filling into batter using a figure-eight motion. Sprinkle evenly with streusel topping.
6. Bake until muffin tops are golden and just firm, 17 to 19 minutes, rotating muffin tins from front to back halfway through baking time. Cool muffins in muffin tins for 5 minutes, then transfer to a wire rack and cool 5 minutes before serving.