Preheat oven to 350. Line baking sheets and set aside
Combine flour, cocoa powder, baking powder, cornstarch and salt in a small bowl. Set aside.
Cream butter, granulated sugar and brown sugar together in mixer until creamy and smooth. About 1 to 2 min.
Whisk in egg, vanilla, vinegar and food coloring until combined.
Add dry ingredients and mix until just combined. Do not over mix.
Using medium cookie scoop, scoop cookies out onto prepared cookie sheets. You should get about 24 cookies.
Lightly press down tops of cookies to flatten.
Bake cookies for 10 min.
Cool cookies for about 15 min on cookie sheet before removing to a cooling rack.