Cocoa Cream Pie

1 graham cracker pie crust

3/4 cup sugar

1/4 cup baking cocoa

3 Tbsp cornstarch

1/4 tsp salt

2 cups milk

2 egg yolks, beaten

1 Tbsp butter

1 tsp vanilla

Stir together, sugar, cocoa, cornstarch and salt in a saucepan.  Gradually stir in milk.  Cook over medium heat, stirring constantly, until mixture is thickened and bubbly.  Boil 1 minute; remove from heat.  Gradually stir about half of the hot filling into yolks.  Return all to saucepan; heat to gentle boil.  Cook and stir for 1 minute.  Remove from heat.  Stir in butter and vanilla.  Pour into crust.  Press plastic wrap directly onto surface (to eliminate film from developing).  Cool.  Refrigerate until set, about 4-6 hours.