1. In a large pot, melt the butter over moderately low heat. Add the onion and sage and cook, stirring occasionally, until the onion is translucent, about 5 minutes.
2. Add the sweet potatoes, broth, and 1 teaspoon of the salt. Bring to a boil. Reduce the heat and simmer until the sweet potatoes are tender, about 10 minutes.
3. Transfer half the soup to a food processor or blender and puree. Return the pureed soup to the pot and add the green beans, the remaining teaspoon salt, and the pepper. Simmer until the beans are just tender, about 8 minutes.
4. Stir in the strips of turkey. Cook until the turkey is just done, about 1 1/2 minutes.
Turkey Options: If you like, buy a three-quarter-pound piece of cooked turkey breast from the deli to use instead of the turkey cutlets. Cut the turkeyinto half-inch cubes and heat it in the soup briefly. Another option is to use leftover cooked turkey or chicken. About two cups of cubed leftovers should do it.
Wine Recommendation: Sweet wines are said not to work at the table, but when the dish contains sweet elements, the wine often should, too. A cool glass of succulent auslese riesling from the Rheingau will prove the point quite elegantly.