Preheat oven to 425°F, and grease your donut pans. I brush my pans with vegetable oil.
In a small bowl, combine milk, 2½ tsp of vinegar, and red food colouring. Stir and set aside for 5-10 minutes to thicken.
Sift and lightly whisk together flour, cornstarch, baking powder, baking soda, salt, cocoa powder, and sugars.
Combine melted butter, 1 tbsp vinegar, applesauce, and vanilla in a small bowl or measuring cup. Add to dry ingredients and stir, or mix on low for about 30 seconds, until just combined. Batter will resemble sandy crumbs.
Add the thickened red milk to the batter and mix on medium-high speed, about 30 seconds, until combined. Batter should be smooth and spoonable, like a thick pancake batter.
Fill donut molds ¾ full, no matter what type of donut molds you use. I usually use a cookie scoop to spoon batter into molds and then spread the mounds out evenly.
Bake at 425°F for 5 minutes (this makes a nice round top when they bake), then lower oven temperature to 350°F without opening the oven until the donuts are done (timing below). Bake until a toothpick comes out clean, or the tops are firm and spring back to the touch.
For large 4″ donuts: bake at 350°F for an additional 12-15 minutes.
For mini 1″ donuts: bake at 350°F for an additional 6-8 minutes.
Cool in pans completely before trying to take out of the molds, at least 15 minutes. This allows them to firm up and release easier.
Once cooled, drizzle or dunk the donuts in a simple icing sugar glaze, like this one – I highly recommend using the cream cheese glaze!