Margaret's Southern Chocolate Pie

Preheat the oven to 350 degrees F (175 degrees C). Sift flour and cocoa powder together into a saucepan.

Whisk 1 1/3 cups sugar and egg yolks together in a bowl. Gradually add evaporated milk, whisking constantly. Slowly pour milk mixture into the saucepan, whisking until combined with flour mixture.

Cook over medium heat, stirring constantly with a flat-bottomed wooden spoon or spatula, until mixture begins to thicken and coats the back of the spoon, about 15 minutes. Remove custard from the heat and stir in butter until melted. Pour into pie crust.

Beat egg whites and cream of tartar in a clean glass or metal bowl with an electric mixer until foamy. Gradually add remaining 6 tablespoons sugar, a tablespoon at a time, continuing to beat until stiff peaks form. Spread meringue over chocolate filling.

Bake in the preheated oven until the tips of the meringue peaks are golden brown, about 10 minutes.