Place 1/2 teaspoon saffron threads in 1/4 cup hot water and set aside for 30 - 40 minutes to steep. Peel and cube 3 medium onions, (approximately 3cups). Place in a large saucepan with 2 to 3 tablespoons water, cover and le sweat over low heat for 5 to 6 minutes until transparent. Watch carefully, d not let burn. Peel and cube 3 medium potatoes(approximately 4 cups)and add onions along with 6 cups chicken broth. Bring to a simmer and cook for 25 t 30 minutes until tender. Put through a food mill, or puree in a food process or blender. Return to pan and stir in 1 cup of heavy cream together with th saffron water. Heat before serving but do not boil. Check for seasoning, and serve topped with additional cream that has been whipped and thin slices o lemon. Serves 6.