In a large mixing bowl, combine flour, powdered sugar, and a pinch of salt. Cut in cold diced butter until the mixture resembles coarse breadcrumbs. Add an egg and mix until dough forms. Wrap in plastic wrap and chill for 30 minutes.

Preheat your oven to 180 °C (350 °F). Roll out chilled dough to about 3 mm thick and fit into tartlet molds. Prick the bases with a fork. Blind-bake for 15 minutes, then set aside to cool slightly.

In a saucepan, heat cream over medium heat until boiling. Stir in chopped dark chocolate and mix until smooth. In a separate bowl, whisk together eggs, sugar, and vanilla, then fold into the chocolate mixture.

Pour the chocolate filling into cooled tartlet shells, filling them about three-quarters full. Bake for an additional 10-15 minutes, checking for a slight jiggle in the center.

Allow tartlets to cool in the molds for 10 minutes, then transfer to a wire rack to cool completely.