Preheat the oven to 350°F. Spray a 9X9-inch pan (or 8X8-inch pan for thicker brownies) with baking nonstick spray. Line the bottom and 2 sides of the pan with parchment paper. Then, spray again.
In a medium bowl, mix the flour, cocoa powder, cornstarch, and salt. Set aside.
1 ¼ cup All-purpose flour, ⅓ cup Unsweetened cocoa powder, 1 tablespoon Cornstarch, 1 teaspoon Salt
Using a mixer with a whisk attachment, beat the sugar, eggs, and egg yolk on high speed for 5 minutes. It will become very pale in color.
2 cups White granulated sugar, 3 Large eggs, 1 Large egg yolk
Add the melted butter, oil, vanilla, and red food dye. Mix on low until just combined. Add in the dry ingredients and mix until just combined.
½ cup Oil, ½ cup Unsalted butter, 1 teaspoon Pure vanilla extract, 1 teaspoon Red food dye
Take off the mixer, and add in the white chocolate chips. Use a rubber spatula to fold them in. Pour the batter into the pan.
1 ½ cups White chocolate chips
Bake for 45-50 minutes. Bake until a toothpick inserted comes out with moist crumbs. If still raw, bake for another 5 minutes.
Let the brownies cool completely in the pan on a cooling rack before cutting into them.