Preheat oven to 375 degrees. In a medium mixing bowl, combine flour, cocoa powder, cornstarch, baking soda, and salt. Set aside.
In another mixing bowl or stand mixer, cream together the butter, shortening, and sugar for about 3 minutes until fluffy. Slowly add in the egg yolk and egg and mix to combine. Add vinegar, vanilla, and food coloring and mix until just combined.
Add in the dry ingredients until combined. Mix in 1/2 cup white chocolate chips.
Line cookie sheets with parchment paper and scoop out the cookie dough into heaping tablespoons. Be careful not to flatten the cookies.
Bake for 8-9 minutes in the preheated oven. Transfer to a wire rack to cool and press extra chocolate chips on top. Keep the cookies stored in an airtight container.