Make the Crust:
Preheat your oven to 350°F (175°C).
In a medium bowl, combine the vanilla wafer crumbs and melted butter. Stir until the crumbs are evenly coated.
Press the mixture into the bottom and up the sides of a 9-inch pie dish.
Bake the crust for 10 minutes, then remove from the oven and let it cool completely.

Make the Filling:
In a saucepan, melt the butter over medium heat. Add the cinnamon and Mexican hot chocolate discs. Stir until the chocolate melts and the mixture is smooth.
Gradually add the milk, stirring continuously. Bring the mixture to a simmer.
In a separate bowl, whisk together the sugar, egg yolks, cornstarch, and cocoa powder until smooth.
Slowly pour the hot milk mixture into the egg mixture, whisking constantly to avoid curdling.
Return the mixture to the saucepan and cook over medium heat, stirring constantly, until it thickens to a custard-like consistency (about 5-7 minutes).
Remove from heat and pour the filling into the cooled crust. Allow it to cool to room temperature, then refrigerate for at least 4 hours to set.

Make the Topping:
In a mixing bowl, whip the heavy whipping cream and powdered sugar together until soft peaks form.
Spread the whipped cream over the chilled pie, smoothing it into an even layer.
Garnish with sliced almonds if desired.