Preheat the oven to 350 °F. In a small bowl, stir together the milk and vinegar. Set aside. (See note)
In a large mixing bowl, beat together the butter and sugar until light and fluffy.
Add the egg, vanilla, and milk & vinegar mixture. Mix until combined.
In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt.
Add the dry ingredients to the wet ingredients. Mix until just combined. Add red food coloring. Mix well until all food coloring is evenly distributed.
Chill dough for 30 minutes.
Scoop approx. 1 tbsp of dough into your hands and shape into a ball. Place onto an ungreased baking sheet and bake for 10 minutes. Let cool completely before frosting.