Put the gelatine in a bowl with 4 tbsp of cold water and set aside for a few minutes until it becomes spongy Heat the chicken stock in a pan, add the gelatine and stir until dissolved. Do not allow it to boil over or the gelatine will become stringy. Peel, half and stone the avocado, setting aside one of the halves for garnish. Mash the avocados with the lemon juice and then mix in half the Mayonnaise, cream, and salt and pepper to taste. Stir in the gelatine mixture and pour into a 3 pint ring mould. Chill until set. Garnish with the reserved avocado, cut into slices or cubes.