Preheat the oven to 350°F. Line a standard muffin pan with 12 cupcake wrappers. Set aside.

Start by making the cupcake batter. In a medium bowl, stir together the flour, baking powder, baking soda, and salt with a whisk.

In a separate large bowl, whisk the oil and sugar until the sugar is fluffy.

Add the egg whites and peppermint extract and whisk until combined, then pour in the milk and stir.

Carefully fold in the flour mixture until everything is just mixed. Some small lumps are fine.

Pour about a third of the batter into a separate bowl. Add the red gel food coloring and stir until it is evenly mixed.

Spoon a heaping tablespoon of the white batter into each cupcake wrapper. Then, spoon 2 teaspoons of red batter over the white batter, and top off with 1 more teaspoon of white batter on top.

Bake the cupcakes for 13 to 15 minutes or until a toothpick inserted into the center cupcakes comes out clean. Place on a cooling rack to rest.

While the cupcakes are cooling, make the buttercream. Cream the butter in a large bowl with an electric hand mixer.

Add the peppermint extract, and gradually mix in the powdered sugar until the buttercream is thick.

Pour in the 2 tablespoons of milk to make the buttercream more creamy, then add the salt, if desired, to balance out the sweetness.

Transfer the buttercream to a piping bag with a large star tip, and pipe the frosting onto the cooled cupcakes. Decorate with peppermints, crushed candy canes, or peppermint kisses.