Simmer the prunes, covered, in the tea and Armagnac with the lemon juice and sugar until soft (about 15 to 20 minutes). Puree in the food processor and add more sugar if necessary. Cool.
Whip the heavy cream and fold it into the prunes. Whip the egg whites and fold them into the prunes. Pour into a serving dish or individual dishes and chill for one to two hours before serving. YIELD 4 servings.