Soak the gelatin in the ¼ cup of cold water. Dissolve it in the 1 cup hot water. Add the sugar and salt and stir until dissolved. Add the lemon juice, vinegar, mayonnaise and pepper. Blend with a rotary beater. Pour into a refrigerator tray and chill until firm one inch from the edge (about 25 minutes).
Whip with the beater until fluffy. Fold in the spinach, cottage cheese, celery and onion. Pour into individual molds and chill in the refrigerator for about 1 hour.