Lemon Sugar Topping ~
1/3 cup granulated sugar
finely grated zest from 1 lemon
2 cups blueberries
1 1/8 cups sugar plus 1 teaspoon
2 1/2 cups flour
2 1/2 teaspoons baking powder
1 teaspoon salt
4 tablespoons unsalted melted butter
1/4 cup vegetable oil
1 cup buttermilk
2 teaspoons vanilla extract
For the topping:
Stir together sugar and lemon zest in a small bowl
Preheat oven to 425 degrees.
Spray jumbo muffin tin with nonstick cooking spray.
Bring 1 cup of blueberries and 1 teaspoon of sugar to simmer over medium heat in a small saucepan. Mash the berries and stir often until the berries have broken down and mixture is thickened and reduced to 1/4 cup. This should take about 5~8 minutes, cool to room temperature.
Whisk together the flour, baking powder, and salt in a large bowl. In a medium bowl, whisk 1 1/8 cups of sugar and eggs until thick (~45 seconds). Slowly, whisk in the butter and oil until combined. Next, whisk in buttermilk and vanilla. Fold the egg mixture and remaining cup blueberries into flour mixture, until just moistened. Be careful not to overmix.
Transfer the batter to muffin cups so that the batter completely fills the cups. Next, add a teaspoon of the cooked berry mixture into the center of each mound of batter. Use a toothpick to gently swirl the berry filling into the batter. Then, sprinkle the lemon sugar crumble evenly over the muffins.
Bake for 20~23 minutes, or until the muffin tops are golden. Cool the muffins in tin for around 5 minutes, then transfer to wire rack and cool for an additional 5 minutes before serving