Preheat your oven to 350°F (175°C). Line two 12-cup muffin tins with paper liners. In a medium bowl, whisk together the flour, cocoa powder, and salt.
In a large bowl with an electric mixer, beat the 1/2 cup of softened butter and granulated sugar on medium-high speed until pale and fluffy, about 3-4 minutes. Beat in the eggs one at a time, followed by the vanilla, 1 teaspoon of peppermint extract, and red food coloring.
Reduce the mixer speed to low. Add the flour mixture in three parts, alternating with the buttermilk in two parts, beginning and ending with the flour. Mix just until combined; do not overmix.
In a small bowl, stir the baking soda and apple cider vinegar together. The mixture will fizz. Immediately fold it into the batter until just incorporated.
Divide the batter evenly among the prepared cupcake liners, filling each about two-thirds full. Bake for 12-15 minutes, or until a wooden skewer inserted into the center of a cupcake comes out clean.
Let the cupcakes cool in the pans for a few minutes before transferring them to a wire rack to cool completely. Cupcakes must be fully cool before frosting.
To make the frosting, beat the softened cream cheese and the other 1/2 cup of softened butter in a large bowl until smooth. With the mixer on low, gradually add the sifted powdered sugar. Add the remaining 1 teaspoon of peppermint extract and 2 tablespoons of milk. Beat on medium-high until the frosting is light and creamy, adding more milk if needed to reach a spreadable consistency.
Pipe or spread the frosting onto the cooled cupcakes. Garnish with a sprinkle of crushed peppermint candies before serving.