Blueberry Swirl Muffins

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

1. FOR THE TOPPING: Stir together sugar and lemon zest in small bowl until combined and set aside.
2. FOR THE MUFFINS: Adjust oven rack to upper-middle position and heat oven to 425 degrees. Spray 12-cup muffin tin with vegetable oil 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 1⁄4 cup, about 6 minutes. Transfer to small bowl and let cool to room temperature, 10 to 15 minutes.
3. Whisk flour, baking powder, and salt together in large bowl. Whisk remaining 1-1⁄8 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 1 cup blueberries into flour mixture until just moistened. (Batter will be very lumpy with few spots of dry flour; do not overmix.)
4. Using ice cream scoop or large spoon, divide batter evenly among prepared muffin cups (batter should completely fill cups and mound slightly). Spoon 1 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 muffins are golden brown and toothpick inserted in center of muffin comes out with few crumbs attached, 17 to 19 minutes, rotating muffin tin halfway through baking. Let muffins cool in tin for 5 minutes, then transfer to wire rack and let cool for 5 minutes before serving.

BLUEBERRY SWIRL MUFFINS WITH FROZEN BLUEBERRIES
Substitute 8 ounces frozen blueberries for fresh blueberries. Cook 1 cup blueberries as directed in step 2. Rinse remaining berries under cold water and dry well. Proceed with recipe from step 3 as directed.

BLUEBERRY SWIRL MUFFINS WITH STREUSEL TOPPING
Omit Lemon-Sugar Topping. Instead combine 3 tablespoons granulated sugar, 3 tablespoons packed dark brown sugar, pinch salt, and 1⁄2 cup plus 3 tablespoons all-purpose flour in small bowl. Drizzle with 5 tablespoons warm, melted unsalted butter and toss with fork until evenly moistened and mixture forms large chunks with some pea-size pieces throughout. Proceed with recipe as directed, sprinkling streusel topping over muffins before baking.

BLUEBERRY SWIRL MUFFINS WITH ORANGE GLAZE
Turbinado sugar is often sold as Sugar in the Raw.
Omit Lemon-Sugar Topping. Add 2 teaspoons grated orange zest to egg mixture. Proceed with recipe as directed, sprinkling 4 teaspoons turbinado sugar over muffins before baking. While muffins cool, whisk together 1 cup confectioners’ sugar and 1-1⁄2 tablespoons orange juice until smooth. Drizzle each cooled muffin with 2 teaspoons glaze before serving.

BLUEBERRY SWIRL MUFFINS WITH ALMOND CRUNCH TOPPING
Turbinado sugar is often sold as Sugar in the Raw.
Omit Lemon-Sugar Topping. Instead combine 1⁄3 cup finely ground almonds and 4 teaspoons turbinado sugar in step 1 for topping and set aside. Add 1⁄3 cup finely ground almonds to flour mixture. Proceed with recipe as directed, adding 1 teaspoon almond extract to batter with vanilla extract and sprinkling almond topping over muffins before baking.