Preheat the oven to 350 degrees F. Bake pie shell until just golden around edges, about 12 minutes; set aside.
In a medium bowl set over a saucepan of simmering water, combine chocolate and butter. Cook, stirring, until melted and combined, 5 to 8 minutes; keep warm.
In a medium bowl, whisk egg yolks and 2 tablespoons sugar until stiff peaks form. In a second bowl, whisk the egg whites and a pinch of sugar until frothy, then slowly beat in the remaining sugar and whip just until stiff peaks form. Fold the yolk mixture into the chocolate mixture until partially combined; fold into half of the white mixture. Add the remaining whites and fold until combined.
Scoop the mixture into the pie shell; fill to the top of the shell. Bake until the pie doubles in size, has a crust on top, and is cake-like on the outside, but still soft in the center, about 20 minutes.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Adapted from a recipe courtesy Mindy Segal, Hot Chocolate, 2011