Preheat oven to 350° F. Prepare donut pan by spraying with non-stick cooking spray; set aside.
In large bowl, or stand mixer, mix together all-purpose flour, baking soda, salt, cocoa powder, and sugar until combined. Add milk, oil, egg, red food coloring, vanilla, and vinegar. Mix until combined and batter is smooth.
Pour batter into gallon-sized ziploc bag and cut off small triangle from the corner. Pipe batter into prepared donut pan until about 1/2 full.
Bake at 350° F for 10-12 minutes or until donuts are set. Pull out of oven and let cool in pan for about 10 minutes then transfer to wire rack to cool completely.
While donuts are cooking and cooling, mix powdered sugar, cream cheese, vanilla, and milk in small bowl until combined.
Add frosting to another ziploc bag with corner cut off (or icing bag) and decorate donuts using back and forth motion, or as you would like to.