Oven 325
Drain cherries, preserving 1/2 c liquid. Transfer cherries to a medium saucepan. Add reserved cherry liquid, the 1/2 c sugar, and the tapioca. Cook and stir over medium heat until mixture boils; reduce heat. Simmer, uncovered, for 5 minutes, stirring constantly; keep warm.
In a medium mixing bowl beat egg whites, cream of tartar, and salt with an electric mixture on medium speed until stiff peaks form (tips stand straight), set aside. In a small mixing bowl beat egg yolks for 2-3 minutes or until thick and lemon coloured, add the 1/3 c sugar. Beat 1 minute more. Stir a small amount of egg white mixture into egg yolk mixture to lighten. Fold remaining egg yolk mixture into egg white mixture. Sprinkle flour over egg mixture, fold in.
Pour hot cherry mixture into a 1 1/2-quart casserole or into six 6-8 ounce casseroles or custard cups. Pour batter over cherry mixture. Bake in a 325 degree oven for 35-40 minutes for the 1 1/2 quart casserole for about 30 minutes for the small casseroles or custard cups or until top springs back when lightly touched. Serve warm.