Combine mayonnaise and flour, mix well. Gradually add milk; cook stirring constantly over low heat until thickened. Add salt and cheese, continue cooking until cheese melts. Cool slightly; stir in broccoli and slightly beaten egg yolks. Fold in stiffly beaten egg whites; pour mixture into 1-1/2 quart casserole. With tip of spoon, make slight indention around top of souffle to form a top hat. Bake at 300° for 10 hour and 15 minutes. Serve immediately.