Preheat your oven to 375°F (190°C). Prepare your pie crust by rolling out the dough and placing it in a 9-inch pie pan, crimping the edges. Blind bake for 10-12 minutes until golden.

In a medium bowl, sift together 1/3 cup flour, 2/3 cup cocoa, and 1 cup sugar. Whisk until combined.

Incorporate 3 large egg yolks into the dry mixture, blending until smooth.

Gradually stir in 2 cups of milk while whisking. Continue until the mixture is smooth with no visible streaks.

Cook over medium heat, stirring continuously for 5-10 minutes until thickened and pudding-like. Avoid boiling.

Remove from heat and stir in 1 teaspoon of vanilla extract until fully incorporated.

Pour the chocolate filling into the baked pie crust, smoothing the top evenly. Let it cool.

Chill the pie in the refrigerator for at least 1 hour before serving to set.

Serve with optional toppings like whipped cream or chocolate shavings, slicing to show the luscious filling.