01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt.
03 - In a separate bowl, whisk eggs, milk, vegetable oil, vanilla, and peppermint extract until fully combined.
04 - Pour wet ingredients into dry ingredients and mix until just combined.
05 - Stir in boiling water carefully; the batter will be thin.
06 - Divide batter evenly among liners, filling each about two-thirds full.
07 - Bake for 16 to 18 minutes or until a toothpick inserted in the center comes out clean.
08 - Allow cupcakes to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
09 - Beat softened butter until creamy. Gradually add powdered sugar, milk, peppermint extract, and salt. Beat until light and fluffy.
10 - Pipe or spread buttercream onto cooled cupcakes and sprinkle with crushed candy canes.