Saute onions in oil until lightly browned. In a large pot, combine half of the onions with the salt, half ts rosemary, sweet potatoes & 1.5 c stock. Cook until potatoes are tender. Cool to room temperature & blend with milk & hazelnut butter until very smooth. Set aside. Combine remaining onions, mushrooms, tamari, pepper, remaining rosemary & 2 tb water. Cook for 5 minutes. Add to sweet potato mixture & simmer for 5 minutes. Serve hot over fresh pasta. NOTE Only use fresh shiitake mushrooms.