Combine Butter and Oil: Add the melted, cooled butter and neutral cooking oil to a large mixing bowl. Whisk until the two fats are thoroughly combined.
Add the Sugar: Whisk the granulated sugar into the butter mixture until evenly incorporated.
Mix the Eggs and Vanilla: Add the egg, egg white, and vanilla extract. Whisk vigorously until the mixture is thoroughly combined.
Add the Buttermilk: Gradually whisk the buttermilk into the wet mixture until fully incorporated.
Prepare the Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, baking powder, cornstarch, and salt until evenly distributed.
Combine the Batter: Gently fold the dry ingredients into the wet mixture. Avoid over-mixing. When approximately half of the dry ingredients have been incorporated, add the chopped strawberries and continue folding gently until the batter is just combined.
Rest the Batter: For a higher muffin top, cover the bowl with a dry towel and let the batter rest for 30–60 minutes before baking. This step is optional; the muffins can also be baked immediately.
Prepare the Oven and Tin: Preheat the oven to 425°F (215°C). Line a 12-count muffin tin with paper liners.
Fill the Muffin Tin: Once the oven has reached temperature, divide the batter evenly among the prepared muffin liners. The recipe can make 12 muffins, while dividing the batter among 9 liners will produce larger, bakery-style muffins. Add the Sugar Topping: Sprinkle a small amount of coarse sugar over the top of each filled muffin.
Bake at High Temperature: Place the muffin tin on the center rack of the preheated 425°F (215°C) oven and bake for 8 minutes.
Lower the Oven Temperature: Without opening the oven door, reduce the temperature to 350°F (175°C). Continue baking for another 10–12 minutes, or until the muffin tops are just beginning to turn golden brown.
Cool the Muffins: Let the muffins cool in the tin for 5–7 minutes. Carefully remove them from the tin and transfer them to a cooling rack. Allow them to cool completely before serving.
