How to Make It
In the bowl of a standing electric mixer fitted with the paddle, blend 1 cup of all-purpose flour with the butter, sugar, cocoa, almond flour and salt at medium speed. Mix in the egg just until a soft dough forms. Scrape the dough onto a large sheet of plastic wrap and lay another large sheet of plastic wrap on top. Roll out the dough between the plastic wrap to a 12-inch round. Transfer the round to a baking sheet and freeze until firm, 10 minutes. Preheat the oven to 325°.
Peel off the top sheet of plastic and invert the dough onto a 10-inch fluted tart pan with a removable bottom. Remove the remaining sheet of plastic and gently press the dough into the pan. Trim the dough flush with the rim. Freeze until firm, 10 minutes.
Line the tart shell with parchment paper and fill with pie weights or beans. Bake in the center of the oven for 30 minutes, until the tart shell is nearly cooked through. Remove the parchment and weights and bake until the shell is cooked through, about 20 minutes longer. Transfer to a rack and let cool. Lower the oven temperature to 250°.
In a medium saucepan, combine the cream and milk and bring to a boil. Remove from the heat. Add the chocolate and let stand until melted, 5 minutes. Whisk until smooth. In a small bowl, whisk the egg with the egg yolk, then whisk in 1/2 cup of the chocolate cream. Thoroughly whisk this custard into the chocolate cream in the saucepan. Pour the filling into the tart shell and bake until set around the rim but still slightly jiggly in the center, 30 minutes. Let the tart cool on a rack for 10 minutes, then refrigerate until chilled, 2 hours.
In a small bowl, sprinkle the gelatin over the milk and let stand 5 minutes. In a small saucepan, whisk the cream, sugar and cocoa over moderate heat until the sugar is dissolved, 2 minutes. Remove from the heat. Scrape the gelatin into the cocoa mixture, add the milk chocolate and whisk until melted. Pour the glaze over the tart and spread it in an even layer using an offset spatula. Refrigerate the tart until the glaze is firm, 30 minutes. Serve with whipped cream.
Almond flour, made from finely ground blanched almonds, can be found at most gourmet and health-food stores.