Preheat oven to 350 degrees. Line standard muffin tins with paper liners. Whisk together flour, cornstarch, cocoa, and salt.
With an electric mixer on medium-high speed, whisk together sugar and oil until combined. Add eggs, one at a time, beating until each is incorporated, scraping down sides of bowl as needed. Mix in vanilla and food color, adding a little color at a time til desired color is achieved.
Reduce speed to low and add in the flour mixture and buttermilk a little at a time. Stir together the baking soda and vinegar in a small bowl (it will foam) then add the mixture to the batter, and mix on medium speed 10 seconds.
Fill each cupcake cup to 3/4 full. Bake until a knife inserted in centers comes out clean, about 20 minutes.
Transfer tins to wire racks to cool completely before removing cupcakes.
Cupcakes can be stored overnight at room temperature, or frozen up to 2 months, in airtight containers. Make a buttercream or cream cheese frosting to top the cupcakes.
