Preheat the oven to 200 °. Cut the white chocolate into small cubes. Melt the dark chocolate in a cup in a double boiler. Put 2 paper baking cases, one inside the other, ready.
Mix the fat with sugar and egg yolk until frothy and stir in melted chocolate.
Beat the egg whites with a pinch of salt until stiff and place on the egg yolk cream. Sift the flour over it and fold in with a wooden spoon. Finally add white chocolate chips.
Pour the dough into the prepared molds and bake on the middle rack for 15-20 minutes. Then let cool down completely.
Before serving, whip the whipped cream with vanilla sugar until stiff and serve with the tartlets. Dust very thinly with powdered sugar.