Adjust oven rack to upper-middle position and heat to 425 degrees F. Spray standard muffin tin with nonstick cooking spray. Use cupcake liners if desired.
Whisk flour, baking powder, and salt together in a large bowl, set aside.
In a separate, medium-sized bowl, whisk remaining 1 1/8 cups sugar and eggs together until thick and homogenous, about 45 seconds. Slowly whisk in butter and oil until combined. Whisk in buttermilk and vanilla until combined.
Using a rubber spatula, fold egg mixture and remaining cup blueberries into flour mixture until just moistened. Batter will be very lumpy with a few spots of dry flour; do not overmix.
Use an ice cream scoop or large spoon to divide batter equally among prepared muffin cups. Batter should completely fill cups and mound slightly.
Spoon a 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 figure-eight motion.
Sprinkle lemon sugar or streusel topping 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 pan for 5 minutes, then transfer too wire rack and cool 5 minutes before serving.