This is the recipe I use. I got it from a 1963 McCalls Cookbook.
Chocolate Merengue Pie
9-inch pie shell
1 cup sugar
5 tablespoons cornstarch
5 tablespoons sugar
2 oz. unsweetened chocolate
1 teaspoon salt
2-1/2 cups milk
3 egg yolks, slightly beaten
1/2 teaspoon vanilla extract
1/2 teaspoon almond extract
3 egg whites at room temperature
1/4 teaspoon cream of tartar
6 tablespoons sugar
Prepare and bake pie shell; let cool.
Make filling:
In medium saucepan, combine sugar, cornstarch, chocolate, and salt; mix.
Gradually stir in milk, mixing until smooth.
Over medium heat, bring to boiling, stirring; boil 1 minute, stirring constantly. remove from heat.
Stir half of hot mixture gradually into the egg yolks, mixing well; pour back into saucepan. (Stir egg yolks vigorously or you'll end up with scrambled egg in chocolate.)
Bring back to boiling, stirring; boil 1 minute longer. remove from heat.
Stir in extracts; pour immediately into pie shell.
Meanwhile, preheat oven to 400F.
Make meringue:
In medium bowl, with portable electric mixer at medium speed, beat egg whites and cream of tartar until soft peaks form when beater is raised.
Gradually beat in sugar, 2 tablespoons at a time, beating well after each addition. Continue to beat until stiff peaks form when beater is raised.
Spread meringue over warm filling, sealing to edge of crust.
Bake 7 to 10 minutes, or until meringue is golden.
Cool on wire rack, away from drafts, 1 hour before serving.