Mix the chocolate shortbread crust ingredients in a food processor until the mixture resembles play dough. Shape into a disk, cover in plastic wrap, and chill for 30 minutes to 2 hours.

Preheat your oven to 375°F (190°C). Roll out the dough to about 1/8-inch thick and transfer to a metal pie plate. Trim excess dough, poke bottom with a fork, and bake for 15–20 minutes.

In a double boiler, melt butter and milk chocolate until smooth. Cool slightly. In a separate bowl, mix eggs, sugar, cocoa powder, and flour; stir in melted chocolate and strain.

Pour the filling into the pre-baked crust and bake at the same temperature for 25–30 minutes, until set around the edges but jiggly in the center.

For the topping, combine egg whites and sugar in a heatproof bowl over a double boiler. Whisk until mixture reaches 160°F (70°C) and sugar dissolves. Whip until stiff peaks form.

Allow the pie to cool at room temperature for about 30 minutes before slicing and serving warm.