Makes 12 muffins
Ingredients: Lemon-Sugar Topping
FOR THE TOPPING
Stir together sugar and lemon zest in small bowl until combined; set aside.
FOR THE MUFFINS
Adjust oven rack to upper-middle position and heat oven to 425°. Spray standard muffin tin with nonstick cooking spray. Whisk flour, baking powder, and salt together in large bowl. Whisk 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 frozen blueberries into flour mixture until just moistened. (Batter will be very lumpy with few spots of dry flour; do not overmix.)
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 Bonne Maman Wild Blueberry Preserves into center of each mound of batter. Using skewer, gently swirl preserves filling into batter using figure-eight motion. Sprinkle lemon sugar evenly over muffins.
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.