Soak the gelatine for 5 min. in ½ cup broth. Beat the egg yolks and stir lightly in the remaining broth, add salt and pepper, cook in top of a double boiler, stirring constantly until thickened to custard consistency. Stir in the dissolved gelatine. Pour this over the chicken until the mousse begins to set. (This operation is speeded up if the chicken is put in a basin stood in cold water or cracked ice.) Then fold in the cream and mayonnaise. Turn into a mould which has been moistened with cold water. Chill until set.
To serve, turn out and garnish with watercress and lettuce.