If using a store-bought crust, follow the package instructions for baking. If making your own, roll it out and fit it into a pie dish, then blind bake until golden.

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

Slowly whisk in the whole milk until the mixture is smooth.

Place the saucepan over medium heat and stir continuously.

Keep cooking until the mixture starts to bubble and thickens, about 5 to 7 minutes.

Remove the saucepan from heat and stir in the butter and vanilla extract.

Carefully pour the chocolate mixture into the prepared pie crust.

Cover the pie with plastic wrap or aluminum foil and refrigerate for at least 4 hours or overnight.