Steps:

1️⃣ Prepare the Filling:
In a saucepan, combine cocoa powder, sugar, flour, milk, egg yolks, vanilla, and butter. Cook over medium heat, stirring continuously until thickened. Pour the filling into the pre-baked pie crust.

2️⃣ Make the Meringue:
Whisk the egg whites with cream of tartar until soft peaks form. Gradually add sugar, continuing to whisk until stiff peaks form. Spread the meringue evenly over the chocolate filling, ensuring it touches the edges of the crust to seal it.

3️⃣ Bake:
Place the pie in a preheated oven at 350°F (175°C) and bake for 10-15 minutes, or until the meringue is lightly golden on top.

4️⃣ Cool and Serve:
Let the pie cool completely before slicing and serving.