best blueberry muffin recipe

1 1/2 cups all-purpose flour - 3/4 cup granulated sugar - 1/2 teaspoon salt - 2 teaspoons baking powder - 1/3 cup vegetable oil - 1 large egg - 1/3 cup milk - 1 teaspoon vanilla extract - 1 cup fresh or frozen blueberries - 2 tablespoons flour (for coating blueberries) - Optional: coarse sugar for sprinkling on top