Celeriac, Apple and Stilton Soup with Apple-Sage Muffins

4 tablespoons ( 1/2 stick) butter1 large onion, coarsely chopped1 1/2 pounds celeriac, cut into small chunks1 potato, Idaho or Yukon Gold, coarsely chopped3 cloves garlic, crushed2 apples, such as Br 1/8burn, Empire or Cox's Orange Pippin, peeled cored and quartered8-9 cups vegetable stock or waterSea salt and freshly ground black pepper3 ounces Stilton cheese, crumbled ( 2/3 cup)Celery leaves, for garnish, optionalCelery seeds, for garnish, optionalSage Apple Muffins, recipe followsMelt the butter in a large saucepan over medium heat. Add the onions, celeriac, potatoes and garlic. Gently sweat the vegetables for 8-10 minutes, being careful not to brown them. Add the apples and enough vegetable stock to cover. Stir in a generous pinch of sea sad and pepper. Bring to a boil, reduce the heat and simmer until the celeriac is tender, approximately 40 minutes. (To test, remove a chunk of the celeriac and press it with the back of a fork. If it crushes easily it is ready.)Ladle the soup, in batches, into a blender and puree until smooth. Return the soup to a clean saucepan over low heat and add the crumbled Stilton, stirring constantly until melted. Serve in warmed soup bowls with celery leaves and seeds scattered on top, if desired. Offer a basket of warm Apple-Sage Muffins on the side.Serves six.Nutrition values per serving: 229 calories, 13 g fat (8 g saturated), 25 g carbohydrates, 3 g fiber, 8 g protein, 31 mg cholesterol, 1,797 mg sodium."Keep it Seasonal" by Annie Wayte (2006 Morrow, $29.95)