Chocolate Pie

2 cups milk
3/4 cup sugar
2 eggs
1 tablespoon flour
1 tablespoon cornstarch
1 tablespoons cocoa
1 tablespoons butter
1 teaspoon vanilla
1 8 inch pie shell

Combine milk, sugar, eggs, flour cornstarch and cocoa. Cook until thick, stirring constantly. Remove from heat and add butter and vanilla. Chill and pour into pie shell. Top with whipped cream and serve.