Combine sugar, flour, cocoa and salt in medium saucepan; stir in milk. Cook over
medium heat, stirring constantly until mixture boils; remove from heat. Stir half
of the mixture into beaten egg yolks; return mixture to sauce pan. Continue cooking
and stirring over medium heat until mixture boils; boil and stir for 1 minute. Remove
from heat and stir in butter and vanilla extract.
Cool for 10 minutes, then pour
into pie shell.
Heat oven to 350 degrees F.
Meanwhile, prepare meringue: In a small mixer bowl, beat egg whites and cream
of tartar until foamy.
Gradually add sugar and beat until stiff peaks form.
this on warm pie filling, carefully sealing to the edges of crust.
Bake for 5 to 8 minutes, or just until meringue is lightly browned.
Cool to room temperature; chill for several hours.