Chocolate Pie

1 1/4 cups granulated sugar
1/2 cup cocoa
1/3 cup cornstarch
1/4 teaspoon salt
3 cups milk
3 tablespoons butter
1 1/2 teaspoons vanilla extract

Combine all dry ingredients; gradually stir in milk while on medium heat and bring to a boil. Boil for 1 minute. Remove from heat and add butter and vanilla extract. Pour into a baked deep dish pie shell. Cover with plastic wrap and chill several hours; then cover with whipped cream and shaved chocolate.