Blueberry Muffins

Heat the Oven - Set the oven rack to the upper middle position. Preheat to 425ºF (218ºC).
Melt the Butter - Melt the butter in a pan or microwave, then cool to room temperature.
Mix the Dry Ingredients - In a large bowl, whisk together the flour, baking powder, and salt.
Mix the Wet Ingredients - In a medium bowl, whisk together sugar and eggs until smooth and pale yellow in color, about 1 minute. Slowly whisk in the cooled melted butter and vegetable oil until incorporated. Whisk in the buttermilk and vanilla.
Make the Muffin Batter - Add the egg mixture and 1 ¼ cups of blueberries to the flour mixture. Gently fold the mixture until the flour is just moistened, with some lumps and flour spots remaining. Do not overmix the muffin batter.
Portion the Batter - Grease the muffin pan with nonstick cooking spray or vegetable oil or line it with paper cups. Fill each opening to the top, about a ⅓ cup per muffin. Sprinkle some sugar over the top of each muffin. Evenly distribute the remaining ¼ cup of blueberries on top, lightly pressing in 2 to 3 berries per muffin.
Bake the Muffins - Bake for 10 minutes. Rotate the pan and bake until golden brown, 6 to 7 minutes.
Cool the Muffins - Cool the muffins in the pan for 5 minutes. Use a spatula to carefully remove them, then transfer them to a wire rack until ready to serve.