Sprinkle the gelatin over the lemon juice in a small saucepan and soak for two minutes. Place saucepan over low heat and stir the mixture until the gelatin is dissolved.
Pour the gelatin mixture into the container of an electric blender. Add the salt, pepper, egg and one-quarter cup of the oil. Cover and blend on low speed. Remove cover and add one-quarter cup of remaining oil, pouring in a slow stream. Add remaining oil alternately with cream, continuing to blend on low speed. If necessary, stop the motor and use a rubber spatula to stir down the mixture.
If mixture starts to thicken before ready to be used, it may be reheated by placing the blender container in hot water and stirring the aspic until it returns to the proper consistency.