Preheat your oven to 350°F (175°C). In a large mixing bowl, mix the devil's food cake mix with eggs, vegetable oil, and water according to the package instructions. Divide the batter evenly into three greased 9-inch round cake pans. Bake for about 30 minutes, or until a toothpick inserted into the center comes out clean. Let cool in pans for 10 minutes before transferring to wire racks.

In a mixing bowl, beat the softened butter until creamy and smooth. Gradually add sifted confectioners' sugar, mixing on low speed. Once combined, add heavy cream and peppermint extract, beating until fluffy—about 3 to 5 minutes. Add green gel food coloring if desired.

Place one cooled cake layer on a serving platter. Spread a layer of peppermint buttercream on top, then add the second layer. Repeat with the third layer and smooth the sides and top with an offset spatula. Chill in the refrigerator for about 15 minutes.

Heat 1 cup of heavy cream in a saucepan until simmering, then pour over 2 cups of chocolate chips in a mixing bowl. Let sit for about 5 minutes to melt the chocolate, then stir until smooth and glossy.

Remove the cake from the refrigerator and pour the ganache over the top, allowing it to drip down the sides. Use a spatula to spread the ganache evenly and garnish with chopped Andes mints.

Let the ganache set for about 20 minutes before slicing. Serve chilled or at room temperature. Store leftovers in an airtight container in the refrigerator for up to 3 days.