In a food processor or blender, combine the sour cream, cottage-cheese, lemon juice, Worcestershire sauce, and onion. Process only until the mixture is smooth -- about 10 seconds.
Place the sherry in a small saucepan. Sprinkle the gelatin over the sherry and let it stand for 3 to 4 minutes to soften. Then stir the mixture over low heat until dissolved. Combine the gelatin mixture and sour cream-cottage cheese mixture in a blender or food processor and mix briefly.
Pour into a lightly greased 2-cup mold. Refrigerate until firm. This will take at least 4 hours.
To unmold, loosen the sides with a knife and invert the mold onto a plate. Top with the caviar. Serve with rye bread or crackers.