Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan or line it with parchment paper.
In a medium bowl, whisk together the all-purpose flour, cocoa powder, cornstarch, baking soda, and salt until well combined.
In a large mixing bowl, beat together the softened unsalted butter, granulated sugar, and brown sugar until light and fluffy using an electric mixer on medium speed.
Mix in the egg, egg yolk, vanilla extract, and red food coloring until fully incorporated into the butter-sugar mixture.
Gradually add the dry ingredient mixture into the wet ingredients while mixing on low speed until just combined; fold in the white chocolate chips gently.
Pour the batter into your prepared pan evenly and bake for approximately 25-30 minutes or until a toothpick inserted into the center comes out clean.