Stir lemon juice into apricot puree.
Whip cream until stiff.
Fold in the apricot puree.
Beat egg whites, adding sugar gradually until very stiff and smooth.
Fold into apricot-cream mixture.
Turn into a 5-cup, buttered casserole, set in a shallow pan of hot water, and bake in a moderate oven (350° F.) for 20 minutes; then reduce heat to 300° F. (slow) and bake 20 minutes longer.
This dessert may also be served uncooked.