Pre-heat oven to 350º F.
Grease two 9-inch round cake pans or 1 – 9x13, with cooking spray and lightly dust with some flour, then set aside.
In mixing bowl, add buttermilk, water, oil, sugar, eggs, baking soda and salt; stir together until it is well combined. Add in flour and cocoa powder and whisk until smooth and there are no lumps.
Pour batter evenly into prepared pan(s).
Bake for 25-35 minutes, depending on size of pans you use; until you can lightly touch the center and it springs back. Cool pans on a wire rack for 10-15 minutes, then remove cake and allow to completely cool on the wire rack. Once the cakes are cooled prepare buttercream.
Buttercream
In a large bowl, I use my Kitchen Aid mixer cream together butter and Nutella. Slowly mix in the powder sugar, one cup at a time beating well after each addition. Beat in the milk and continue mixing until light and fluffy. You may need to add more sugar or milk until you find the right consistency, this varies every time I do the recipe. If you are not going to use the frosting right away keep covered until you are ready to do so.
Place one cake layer on a serving plate, I like to use a cake stand. Evenly, an additional 2 tablespoons of Nutella on top of the first layer of cake, then top with about ½ cup of buttercream, spread the evenly on top of the bottom layer, then add the second cake on top. Frost with the remaining buttercream, spread on the sides and top, make sure the top is even and the sides are completely covered, once you have frosted the cake, set in the fridge, while you prepare the chocolate glaze.
Chocolate Glaze:
In a small sauce pan add the whipping cream and bring to a boil, remove from heat and add in chocolate chips. Do not mix or stir them in, let the chocolate sit for 5 minutes. Stir until smooth. Let it cool for about 15 minutes, then pour over cake, allowing it to slowly drip down the sides. Set the cake in the fridge and let it chill for 30 minutes, until cake is set.
You are now ready to serve. Enjoy!