Wash the cauliflower and break into flowerets. Cook with the lemon juice in a small amount of boiling water until tender. Drain and whirl cauliflower in blender until pureed or force through a food mill. Sauté the onion and celery in the butter for 2 to 3 minutes. Blend in the flour and stir in broth. Cook, stirring, until slightly thickened. Stir in the cauliflower, cream, nutmeg, and salt. Garnish with cheese. Makes about 1 3/4 quarts or 6 servings