Preheat & Prepare Pan: Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan and set aside.
Mix Dry Ingredients: In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, and salt.
Add Wet Ingredients: Add eggs, milk, vegetable oil, and vanilla extract to the dry mixture. Mix until combined.
Incorporate Hot Water: Slowly mix in the hot water until the batter is smooth. The batter will be thin; this is normal.
Bake: Pour the batter into the prepared pan and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Poke Holes & Add Filling: Remove the cake from the oven and allow it to cool for 5-10 minutes. Use the handle of a wooden spoon or a skewer to poke holes evenly across the surface of the cake.
Chocolate Filling: In a microwave-safe bowl, combine the sweetened condensed milk and chocolate chips. Heat in 20-second intervals, stirring in between, until fully melted and smooth. While the cake is still warm pour the mixture over the cake, ensuring it seeps into the holes. Place the cake in the fridge to chill and absorb the liquid.
Whipped Cream Topping: In a large bowl, beat the cold heavy whipping cream, powdered sugar, cocoa powder, and vanilla extract until stiff peaks form. Spread evenly over the cooled cake.
Garnish: Top with chocolate sprinkles and chocolate shavings.
Serve: Slice and enjoy!