1/2 cup cocoa powder
1 1/8 cup granulated sugar
1/3 cup cornstarch
1 tsp salt
3 cups milk
3 tbsp butter
1 1/2 tsp vanilla extract
9-inch baked pie shell
Mix the cocoa, sugar, cornstarch and salt in a medium saucepan. Slowly pour the milk into the cocoa mixture whisking until smooth. Bring to a boil over medium-high heat, whisking constantly. Boil 1 minute then remove from heat. Whisk in the vanilla and butter. Pour into the prepared pie shell.
Cover pie with plastic wrap and chill at least 4 hours.
Before serving, top with sweetened whipped cream or frozen whipped topping that has been thawed.
Sprinkle with chocolate shavings for garnish, if desired.