1. Preheat oven to 325° F. Generously oil two muffin tins.
2. In a large bowl, whisk cake mix with eggs, milk, oil, vanilla, and peppermint until just combined. Divide batter evenly into pans.
3. Bake 15–18 min, or until a toothpick inserted in center of cake comes out clean. Cool in pan 10 min; unmold onto a cooling rack placed on a sheet pan.
4. Meanwhile, for the ganache, measure chocolate chips into a medium bowl. Pour cream into a microwave-safe measuring cup. Microwave on high until mixture is hot and starts to bubble, about 30–45 sec. Pour over chocolate, ensuring chocolate is covered by the cream; let stand for 1 min. Whisk until chocolate is melted and smooth. Refrigerate until slightly thickened and pourable, about 20 min.
5. Drizzle icing over cupcakes. Garnish with toppings, if desired.
