Preheat the oven to 175°C (350°F) and prepare a muffin tray with liners.
In a bowl, mix the flour and salt together and set aside.
In another bowl, beat the butter and sugar with a mixer for 3-5 minutes until light and fluffy.
Add the eggs one at a time to the butter-sugar mixture, mixing briefly after each addition.
Mix the red food coloring, vanilla extract, and cocoa powder until well combined. Add this to the butter mixture and stir until fully incorporated.
Gradually add one-third of the flour mixture, then one-third of the milk, alternating until everything is mixed in.
In a small bowl, mix the baking soda and apple cider vinegar together, then add it to the batter and mix until just combined.
Divide the batter evenly into the prepared muffin tins, filling each about 3/4 full.
Bake for 16–18 minutes or until a toothpick inserted in the center comes out clean.
Allow the cupcakes to cool completely before adding your choice of frosting.