How to Make It
Put 1 cup of all-purpose flour in the bowl of a food processor with 6 tablespoons of butter cut into pieces, 3 tablespoons of confectioners' sugar and a dash of salt. Process for 15 seconds, until well mixed. In a bowl, mix 1 large egg yolk with 1 tablespoon of milk. Add to the processor bowl and process for another 15 seconds, until the dough forms a ball. Roll out the dough immediately or chill it for an hour or so before rolling.
Arrange ten 3-inch fluted tartlet molds on a table. Roll the dough between 2 sheets of plastic wrap to a thickness of 1/4 inch. Remove the top sheet of plastic and invert the dough over the molds. Using your fingers, press the dough through the plastic into the molds. Remove the plastic and trim the excess dough. Refrigerate for a couple of hours. Bake the tartlet shells in a preheated 350° oven for about 20 minutes until golden. Leave the oven on.
Meanwhile, put 5 ounces of chopped bittersweet or semisweet chocolate into a 4-cup glass measuring cup. Add 2/3 of a stick of butter cut into pieces and 2 tablespoons of sugar. Microwave for 1 minute, stir, leave for a few minutes, then microwave again for 1 minute until the chocolate has melted. In a small bowl, mix 1 whole egg and 1 egg yolk. Whisk the eggs into the chocolate.
Divide the chocolate mixture among the 10 tartlet shells. Bake for 5 minutes. The tartlets should be eaten at room temperature, so that the chocolate filling is slightly soft and creamy. Sprinkle with confectioners' sugar and garnish with the Candied Grapefruit Peel.
For a more brownielike texture, bake for 5 minutes more.