Adapted from Cooking Classy
2 1/4 cups all-purpose flour
2 1/2 tablespoons cocoa powder
1 1/2 teaspoons cornstarch
3/4 teaspoon baking soda
1/2 teaspoons salt
8 tablespoons butter, at room temperature
5 tablespoons shortening
1 1/2 cups granulated sugar
1 egg yolk
1 1/2 tablespoons white vinegar
1 1/2 teaspoons vanilla
1 tablespoons red food coloring
8 ounces white chocolate, chopped into chip sized pieces, divided
Preheat oven to 350º. Line cookie sheets with parchment paper and set aside.
In a mixing bowl, whisk together flour, cocoa powder, cornstarch, baking soda and salt, and set aside. In another bowl, beat butter, shortening and sugar till very pale and fluffy. Add egg and egg yolk and mix until combined. Add vinegar, vanilla and food coloring and mix until well blended. Slowly add in dry ingredients and mix just until combined. Carefully mix in 3/4 cup white chocolate chunks.
Scoop dough out by rounded tablespoonfuls and roll into balls and place about 2 inches apart on prepared cookie sheets. Gently press a few of the remaining chocolate chunks into the top of each cookie, then reshape dough into balls if necessary.
Bake for 12-13 minutes. Allow to cool several minutes before removing to a wire rack to cool.
Makes about 2 1/2 dozen cookies.