Preheat your oven to 350°F (175°C) and line a cupcake pan with paper liners.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.
Add the softened butter, eggs, vanilla extract, buttermilk, and peppermint extract to the dry ingredients. Beat with an electric mixer on medium speed for about 2 minutes until the batter is smooth.
Fold in the mini chocolate chips if using.
Divide the batter evenly among the cupcake liners, filling each about 2/3 full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and let the cupcakes cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
While the cupcakes are cooling, prepare the frosting. In a mixing bowl, beat together the softened butter and powdered sugar until creamy.
Add the heavy cream, peppermint extract, and a few drops of green food coloring. Beat until the frosting is light and fluffy, adjusting the consistency with more cream if necessary.
Once the cupcakes are completely cool, frost them generously with the mint frosting and decorate with chocolate shavings or sprinkles.