Mix all the frosting ingredients together for a few minutes with a spatula until combined.
Transfer to an electric stand mixer and mix for 3 minutes on high speed.
Spread over the top of your cooled cake, rising the icing to peaks if you feel so inclined with a fork.
This makes enough frosting for the top of a 22cm cake and for sandwiching two layers of said cake together.
Topping: Bake the hazelnuts at 180 degrees for ten minutes. Tip the hot hazelnuts into a teatowel and rub to remove the majority of the skins.Allow to cool then sprinkle over the cake.