Preheat oven to 350ºF. Spray a 9×13 baking pan with cooking spray.

Put flour, sugar, cocoa, baking powder, baking soda and salt in a bowl and whisk well. Set aside.

In a large bowl, use a hand mixer to mix the buttermilk, oil, eggs and vanilla together. Slowly add in the mix of dry ingredients while the mixer is on low. Add the coffee and make sure everything is combined, scraping the sides of the bowl with a rubber spatula as needed. The batter will be very thin.

Pour the cake batter into the prepared pan and bake for about 30 minutes or until the center of the cake springs back when you touch it (or a toothpick comes out with a few moist crumbs). While the cake is still warm, poke lots of holes all over the cake with a wooden skewer or a fork.

Whisk together the sweetened condensed milk and unsweetened cocoa powder. Then add the heavy cream and evaporated milk. Whisk well.

Slowly pour the milk mixture evenly over the warm cake. Allow the cake to cool completely.

Refrigerate the bowl of a stand mixer (or glass bowl for using a hand mixer) for 10 minutes to get it cold. Sift the powdered sugar and cocoa powder together.

Beat the cold heavy cream in the cold stand mixer bowl using the whisk attachment for 1 minute.

Add half of the sugar/cocoa powder mixture. Beat until it is fully mixed in, then add the remaining sugar mixture. Continue to whip until stiff peaks form and the mixture is spreadable. It should be fluffy and light.

Spread the chocolate whipped cream on the cooled cake. Sprinkle with chocolate shavings. Store in an airtight container in the refrigerator.