Brought this to a potluck and the entire crowd went nuts!

In a medium saucepan, whisk together the sugar, flour, cocoa powder, and salt.

Gradually whisk in the milk until the mixture is smooth.

Cook over medium heat, stirring constantly, until the mixture thickens and comes to a boil.

Reduce the heat to low and cook for an additional 2 minutes, stirring constantly.

Remove from heat and gradually whisk about 1 cup of the hot mixture into the beaten egg yolks.

Return the egg yolk mixture to the saucepan and bring to a gentle boil, stirring constantly.

Cook for 2 more minutes, then remove from heat.

Stir in the butter and vanilla extract until the butter is melted and the mixture is smooth.

Pour the chocolate filling into the pre-baked pie crust.

Cover with plastic wrap, pressing it directly onto the surface of the filling to prevent a skin from forming.

Refrigerate for at least 4 hours or until set.

Before serving, top with whipped cream and garnish with chocolate shavings.

For a deeper chocolate flavor, you can add 2 ounces of melted bittersweet chocolate to the filling. If you prefer a mocha twist, try adding a teaspoon of instant coffee granules to the dry ingredients. For a nutty variation, sprinkle toasted pecans or almonds over the whipped cream topping. To make it extra special, consider using a homemade graham cracker crust instead of a traditional pie crust.