In saucepan, heat soup, stirring; remove from heat.
Beat egg yolks until thick and lemon-colored; stir into soup.
In large bowl, using clean egg beater, beat egg whites until stiff; fold soup mixture into egg whites.
Pour into 2-quart casserole.
Bake at 300°F. for 1 to 1 1/4 hours or at 400°F. for 30 minutes