Prepare the Pan: Spray an 8 × 8-inch baking pan thoroughly with nonstick cooking spray and set it aside. Preheat the oven to 350°F.
Mix the Wet Ingredients: In a large bowl, whisk together the melted butter, eggs, room-temperature buttermilk, and vanilla extract until well comb
Build the Batter: Add the granulated sugar, flour, Dutch processed cocoa powder, baking powder, baking soda, and salt. Stir until the ingredients are about halfway incorporated.
Add the Hot Water: Pour in the hot water and continue mixing until the batter becomes smooth and evenly combined.
Add the Chocolate: Stir in the very finely chopped semi-sweet chocolate, distributing it evenly throughout the batter.
Bake the Cake: Pour the batter into the prepared pan and bake at 350°F for 34–38 minutes, or until the center is set and a toothpick inserted into the middle comes out clean.
Cool Completely: Remove the cake from the oven and allow it to cool completely before adding the milk mixture.
Prepare the Milk Soak: In a large liquid measuring cup, whisk together the evaporated milk, sweetened condensed milk, and chocolate milk until evenly combined.
Poke the Cake: Once the cake is completely cool, use the tines of a fork to poke lots of holes across the entire top surface.
Soak the Cake: Pour the three-milk mixture evenly over the cake, allowing it to soak through the holes and into the cake.
Chill the Cake: Refrigerate the soaked cake for at least 30 minutes before serving.
Whip the Cream: When ready to serve, use a hand mixer to beat the cold heavy cream until soft peaks form.
Finish the Whipped Cream: Add the powdered sugar, Dutch processed cocoa powder, and vanilla extract. Continue mixing until stiff peaks form.
Top the Cake: Spread the chocolate whipped cream evenly over the surface of the chilled, soaked cake.
Garnish and Serve: Add chocolate shavings if desired, then cut the cake into portions and serve cold.
