Preheat your oven to 375°F (190°C).
Line 16 muffin cups with paper liners. If you don’t have liners, you can grease the cups lightly with butter or non-stick spray.
In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until well combined.
In a medium bowl, whisk together the sour cream, eggs, and vanilla extract until smooth.
Add the sour cream mixture to the flour mixture.
Using a rubber spatula, gently stir the mixture just until the ingredients come together and no dry flour is visible. Do not over-mix—the batter will be thick and a bit lumpy.
Gently fold in the melted butter and vegetable oil into the batter. Again, be careful not to overwork the mixture. The batter should remain thick and slightly sticky.
Carefully fold the blueberries into the batter. If you're using frozen blueberries, keep them frozen until you're ready to add them. This helps prevent the color from bleeding into the batter.
Using an ice cream scoop, fill the muffin cups all the way to the top with batter. This ensures that you’ll get a nice dome shape on your muffins as they bake.
Sprinkle about 1 teaspoon of coarse sugar on top of each muffin. This gives the muffins a crunchy, bakery-style sugar crust.