Place a large frypan over medium-low heat. Melt butter then saute rice, risoni, mushrooms, onion and celery. Stir constantly until rice is lightly browned.
Mix in chicken stock, parsley, marjoram, pepper and hazelnuts. Bring to a boil then reduce heat to low, cover frypan and allow to simmer 15 minutes. Remove from heat and let stand 10 minutes before serving.