Stir together sugar, cocoa, and flour together in a microwave-safe bowl.
Add in egg yolks and milk then stir until combined.
Cook in the microwave on full power for 2 minutes. Stir. Cook 3 more minutes. Stir. Continue cooking in 2-minute intervals until thick and pudding-like consistency.
Stir in margarine and vanilla then pour into baked pie shell.
Beat egg whites and cream of tartar in a glass bowl until foamy, add in sugar 1 Tbsp at a time. Beat until stiff peaks form.
Spread on top of pie filling. Bake in 350 degree F oven for 12-15 minutes until browned.
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