Preheat the oven to 350°F. Grease and line three 8-inch cake pans with parchment paper.
In a large bowl, whisk together flour, cocoa powder, sugar, baking soda, baking powder, and salt.
Add buttermilk, oil, eggs, and vanilla extract. Mix until combined.
Gradually add hot water and mix until smooth. The batter will be thin.
Pour the batter evenly into the prepared pans. Bake for 25-28 minutes or until a toothpick inserted comes out clean.
Cool cakes in pans for 10 minutes, then transfer to wire racks to cool completely.
To make the frosting, beat butter until creamy. Add powdered sugar gradually, then peppermint extract, heavy cream, and food coloring if desired.
Frost the cooled cakes, stacking and spreading frosting between each layer.
Top with chopped Andes mints and pipe extra frosting if desired.