I have this old family recipe.
Hazelnut Icing
1 cup brown sugar
1 cup sour cream
3 Tablespoons cold butter
1 cup chopped hazelnuts
Heat sugar and cream together over low heat for a few minutes until thickened. Add butter. Simmer until mixture forms a soft ball when dropped into cold water from a spoon (or use a candy thermometer and cook until soft ball stage is reached). Remove from the stove, cool. Beat until the mixture is very thick, with a fudge-like consistency. Mix in the hazelnuts and immediately frost the cake.
You could try replacing the brown sugar with white and leave out the nuts to see if this is similar to what your BF remembers.
Good luck!