This is a filling I use for stuffing chocolate puffs - should work well for frosting a cake.
6 ounces cream cheese, softened
1 tablespoons granulated sugar (divided)
2/3 cup chocolate-hazelnut spread (Nutella)
1/4 cup whipping cream
1/2 cup chopped toasted hazelnuts or pecans
Beat together cream cheese and granulated sugar in a mixing bowl. Gradually beat in chocolate-hazelnut spread and the whipping cream. Stir in nuts.
For stuffing the puffs, I chill the mixture first and pipe into the puffs. I think for a cake it would be the right consistency for spreading.