Preheat the oven to 325 degrees F and prepare the baking strips by soaking them in water.
Spray three 8-inch round cake pans with cooking spray. Line the base of the pans with a circle of parchment paper and line the sides with a thin strip of parchment.
Combine the dry ingredients by sifting the flour, cocoa, baking soda, baking powder and salt into a large bowl then stir in the sugar.
In a separate bowl combine the wet ingredients. Whisk together the buttermilk, vegetable oil, Nutella, diluted coffee, eggs, and vanilla extract.
Gradually pour the wet mixture into the dry mixture while mixing continuously to prevent any lumps forming. The batter will be quite runny.
Pour the batter evenly between the three pans.
Bake the cakes for 60-70 minutes. Check the cakes after 60 minutes by inserting a toothpick into the center. If it comes out clean or with a few crumbs attached remove the cakes from the oven. If the batter is still wet, bake for a further 5-10 minutes before retesting.
Transfer the cakes to a cooling rack and remove the baking strips. Allow them to cool in the pans for 15minutes, then carefully invert them onto the cooling rack and remove the parchment paper.
Allow the cakes to cool completely before wrapping them in plastic wrap.
Set them aside to assemble the next day or if you are assembling the cake the same day, pop them into the freezer for 30 minutes before you prepare them for stacking.