Bittersweet chocolate and Dutch-process cocoa meld with a shot of fresh brewed coffee to give an ultra-rich flavor to this creamy French silk pie. A frothy meringue is the secret to lightening the brown sugar-sweetened filling.
Preheat oven to 325°F. Coat a 9-inch deep-dish pie pan with cooking spray.
To prepare crust: Combine chocolate wafers and dates in a food processor; process until finely chopped. Add water and oil and process until moistened. Press into the bottom and sides of the prepared pan.
Bake until crisp, about 10 minutes. Cool completely on a wire rack.
To prepare filling and garnish: Combine coffee and water in a small bowl. Sprinkle gelatin on top and set aside to soften.
Whisk egg, milk, 3 tablespoons brown sugar and cocoa in a small saucepan until smooth. Cook over low heat, whisking constantly, until thickened and an instant-read thermometer registers 160°F, 5 to 7 minutes. Do not let the mixture come to a simmer. Remove from the heat. Add the reserved gelatin mixture; stir until dissolved. Add chocolate and vanilla, stirring until melted. Set aside to cool to room temperature, about 30 minutes.
Beat reconstituted egg whites and cream of tartar in a large bowl with an electric mixer on low speed until frothy. Increase speed to high and beat until soft peaks form. Gradually add the remaining 5 tablespoons brown sugar, beating until the meringue is smooth and glossy.
Whisk one-fourth of the meringue into the cooled chocolate mixture until smooth. Scrape the chocolate mixture into the remaining meringue and fold in with a whisk. Spoon the filling into the crust and chill, uncovered, until set, about 3 hours.