A rich and moist pumpkin cake topped with a feather-light buttercream made with Nutella.
In a mixing bowl, combine the eggs, egg white, oil, pumpkin, sugars, and vanilla, and mix until smooth.
In a separate mixing bowl, combine the flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Add to the wet mixture and stir again until smooth.
Divide batter into two greased 7-inch springform (round) pans. Bake at 350 degrees for 40 to 45 minutes or until a toothpick inserted in the cake comes out clean.
Let the cakes cool for at least 30 minutes, then release them from the pans. Carefully trim the top of one of the cakes so that it is perfectly flat. Set aside the cakes and prepare the frosting.
Combine the butter, Nutella, powdered sugar, cream, and salt, and blend until completely smooth. The texture should feel nice and spread-able, not too soft. If necessary, add up to 1/2 cup more powdered sugar to firm it up.
Spread a little less than half the frosting on top of one layer of the cake. Place the second layer on top of the first. Frost the top of the cake, first with an even flat coat, and then with piped decorations as desired.
Garnish the cake with hazelnuts and edible flowers, if desired. Serve or chill until ready to serve.