Put medium sized sauce pan on stove at medium heat. Add 1 cup of sugar, and all of the butter, milk, cocoa, and flour to the pan. Whisk until the mixture is smooth. Continue to stir until whole mixture is thick and creamy. Stir so that it does not burn. Pour into pie crust.
Place egg whites into mixing bowl. Beat on high for 4-5 minutes while gradually adding teaspoons of sugar and the cream of tartar. Meringue is done when mixture is soft and fluffy. Place mixture on top of warm pie.
Place in the oven on 350 degrees F for ten minutes or until warm, golden brown. Wait for pie to cool and then serve.