Preheat oven to 425F (215C) and line a muffin tin with paper liners. Set aside.

In a large mixing bowl, whisk together butter, oil, sugar, egg, egg white, and vanilla extract until thoroughly combined.

Whisk in buttermilk.

In a separate bowl, whisk together flour, baking powder, cornstarch, and salt.

Gently, using a spatula, fold dry ingredients into wet until about 50% combined. Then, add cranberries and white chocolate and continue to gently stir until completely combined.

Evenly divide batter into prepared muffin tin (you can fill them to the top) and sprinkle tops with additional granulated sugar, if desired. For a taller rise, let muffins sit in the tin for 10-30 minutes before baking.

Transfer muffins to center rack of oven and bake for 8 minutes on 425F (215C). Once 8 minutes has elapsed, do not open door, but reduce oven temperature to 350F (175C) and bake another 10-12 minutes or until a toothpick inserted in the center comes out clean or with moist crumbs.

Allow muffins to cool in tin for 10 minutes before carefully removing to a cooling rack to cool completely. Enjoy!