Prep. Preheat the oven to 350℉. Then, lightly grease a 9x13-inch baking dish with nonstick cooking spray.
Mix. In a large mixing bowl, combine the flour, sugar, cocoa powder, baking soda, and baking powder. Whisk well and set aside. Then, in a medium bowl, whisk together the milk, vegetable oil, vanilla extract, and eggs until thoroughly blended.
Combine and add water. Pour the wet ingredients into the dry ingredients. Mix them together gently using a rubber spatula until they are just combined. Slowly pour in the hot water while whisking continuously until the batter becomes smooth and even.
Add cherries. Gently fold in the chopped black cherries until evenly distributed throughout the batter with a spatula.
Bake. Pour the cake batter into the prepared 9x13 baking dish and bake for 30-35 minutes or until a toothpick inserted into the middle of the cake comes out clean. Allow the cake to cool completely in the dish on a wire rack.
Make the frosting. In a large bowl, using a stand mixer or hand mixer, whip the heavy cream until it forms soft peaks. Add the powdered sugar and vanilla extract, continuing to whip until stiff peaks form.
Frost and garnish. Add the whipped cream to the top of the sheet cake and spread evenly. Garnish with shaved chocolate and black cherries. Cut into pieces and serve chilled or at room temperature. Enjoy!