Mom's Chocolate Meringue Pie

Step 1
Make the pie: Mix sugar, cocoa, and cornstarch together in a medium saucepan. Gradually mix in milk. Place over medium-high heat and cook, stirring often, until thickened and bubbly, 4 to 5 minutes. Reduce the heat to medium-low; cook and stir for 2 minutes. Remove from the heat.

Step 2
Preheat the oven to 350 degrees F (175 degrees C). Separate eggs. Set whites aside for meringue.

Step 3
Pour about 1 cup hot filling into egg yolks, whisking quickly to avoid scrambling eggs. Pour mixture back into the saucepan; whisk to combine with hot filling. Set over medium heat and bring to a gentle boil; cook and stir for 2 minutes. Remove from the heat and stir in vanilla. Pour hot filling into crust.

Step 4
Make the meringue: Beat reserved egg whites and cream of tartar in a glass, metal, or ceramic bowl until soft peaks form. Gradually beat in sugar, then continue to beat until stiff peaks form. Spread evenly over hot filling, all the way to the crust.

Step 5
Bake in the preheated oven until meringue is golden, 12 to 15 minutes.