Preheat oven to 350F and butter a 9×13 inch baking pan. If you like, you can line the pan with a parchment sling which makes it easy to remove the cake for frosting and cutting.

Whisk the flour, sugar, cocoa powder, baking soda, baking powder, and salt in a large mixing bowl.

In a separate bowl, whisk together the milk, oil, eggs, and vanilla. Add this to the dry ingredients, and whisk together.

Then add the hot water, and mix until everything is combined, making sure to scrape the sides and bottom of the bowl so no dry bits of flour remain. The batter will be fairly thin.

Pour the batter into your prepared baking pan and bake for 35 minutes. A toothpick inserted into the center should come out without wet batter clinging to it.

Allow the cake to cool fully before frosting.

In a stand mixer with a paddle attachment, cream the butter on medium speed until very smooth.

Add the powdered sugar, a cup or so at a time, and continue to beat until smooth.

Then, slowly add the heavy cream, while the mixer is running on medium speed, and allow it to get fully incorporated.

Add the peppermint extract and food coloring, and mix until everything is smooth and there are no steaks of food coloring left. If your frosting seems too soft or too stiff for your liking, feel free to adjust it by adding either a little more cream to make it softer or a little more powdered sugar to make it stiffer.

Finally, fold in the chopped chocolate.

Spread the frosting on the cooled cake and use the back of a spoon to make pretty swirls.