Preheat the oven to 350 degrees F. Line a muffin pan with cupcake liners.
Whisk together the sugar, flour, cocoa powder, baking powder, baking soda and salt in a medium bowl. Make a well in the center. Add the buttermilk, oil, 1 teaspoon peppermint extract and the eggs to the well and whisk together until there are just a few streaks remaining. Add the chocolate chips and fold them into the batter with a rubber spatula until just combined.
Using an ice cream scoop, fill each cupcake liner about halfway to two-thirds full with batter. Bake until set and a toothpick inserted in the center comes out with just a few a crumbs, about 25 minutes. Allow to cool completely in the pan.
Meanwhile, place the frosting in a medium bowl. Fold in the remaining 1/4 teaspoon peppermint extract, then add the broken candy and fold together using a rubber spatula. Place a dollop of frosting on top of each cupcake and use an offset spatula to spread. Dust the tops with red sprinkles, if using.