Prepare the Oven and Pan: Preheat oven to 170°C. Butter only the bottom of a 9x13 inch baking pan.
Bloom the Cocoa: In a bowl, whisk together hot coffee and cocoa powder until smooth. Let stand for 5 minutes. Stir in the 60 ml of whole milk.
Combine Dry Ingredients: In a small bowl, whisk together flour and baking powder.
Beat Eggs and Sugar: In a large bowl, beat eggs, sugar, vanilla, and salt with an electric mixer on high speed until light and fluffy (about 5-6 minutes).
Combine Wet and Dry Ingredients: Reduce mixer speed to low. Gradually add half the flour mixture, then the coffee mixture, and finally the remaining flour mixture. Mix until just combined, scraping down the sides of the bowl as needed.
Bake the Cake: Pour batter into the prepared pan and bake for 22-25 minutes, or until a toothpick inserted into the center comes out clean. Let cool in the pan for at least 1 hour.
Soak the Cake: While the cake cools, whisk together whole milk and Nutella in a medium bowl. Add whipping cream and evaporated milk. Poke holes all over the cooled cake and slowly pour the milk mixture over it. Allow to soak for 10-30 minutes. Cover and refrigerate for at least 6 hours.
Make the Whipped Cream: In a chilled bowl, beat the whipping cream, icing sugar, vanilla, and salt with an electric mixer until soft peaks form.
In a separate bowl, combine 1 cup whipped cream with Nutella and mix until smooth.
Gradually add the Nutella-whipped cream to the remaining whipped cream, beating on low speed until well combined.
Assemble and Serve: Spread the whipped cream over the cooled cake. Top with sprinkles and chill for at least 30 minutes. Serve cold. Store any leftovers covered in the refrigerator for up to three days.