Add 2 - 3 inches of water to the bottom of double boiler. In top of boiler, combine 1 cup sugar, cocoa, salt and flour. Add egg yolks and milk, stirring until well lmixed. Place double boiler over medium heat and bring water to a gentle boil. Stirring constantly, cook filling 10 - 15 minutes or until thick enough to coat a spoon, like pudding. Remove from heat and cool to room temperature. Preheat oven to 425 degrees.
In medium mixing bowl, beat egg whites on high speed until soft peaks form. Add 6 TBSP sugar, 1 TBSP at a time, beating constantly. Add vanilla. Beat egg whites until stiff and glossy.
Pour filling into baked pie shell. Top with beaten egg whites, being careful to completely cover filling, sealing at edges of crust. Bake for 5 to 8 minutes or until light golden on the peaks. Remove and cool. refrigerate at least 2 hours to set. Makes 8 servings.