Peel and seed squashes. Cut enough into julienne to make 3/4 cup of each. Cover. Cut remaining squash into rough cubes. Chop onion and celery. In a large, heavy saucepan heat the oil with 1-1/2 tablespoons of water. Add cubed squash, onion, and celery. Cover and cook over low heat, stirring occasionally, about 10 minutes. Make a medium roux of butter and flour and cook, stirring constantly (about five minutes). Heat stock and add to roux, stirring briskly until smooth. Combine cooked vegetables with thickened stock and bring to a simmer. Lower heat and cook, partly covered, until very tender (30 to 40 minutes). Puree soup. Grate cheese. Peel and seed apples and cut into thin slices. Stir julienne of squash into soup and heat through (3 minutes). Remove from the heat and stir in cheese and sliced apples. Season to taste.