Soften gelatin in cold water. Put tomato juice in a saucepan with celery leaves, bay leaf, peppercorns, cloves, onion, sugar, salt, Worcestershire, the 1 1/2 tbsp lemon juice and vinegar. Bring to a boil and simmer 10 minutes; strain. Add softened gelatin and stir until dissolved. Chill until thick, but not set.
Peel and halve avocado, then slice crosswise into thin slices and dip each one in lemon juice so they won't brown. Arrange half the avocado slices in a scalloped pattern in the bottom of a 9 inch ring mold. Gently pour in half the thickened aspic; chill until set. Arrange remaining avocado slices in a layer over the molded aspic, and pour in the remaining syrupy aspic mixture. chill until set. Serve with Sour Cream dressing. (See Below)
SOUR CREAM HERB DRESSING:
1/2 pt (1 c) thick cultured sour cream
2 tbsp red win vinegar
1 tsp sugar
1/2 tsp each salt and celery seed
Dash of pepper
1/4 tsp crumbled dried thyme
Combine all ingredients. Turn into a sauce bowl and chill. Makes 1 cup.