1Cream butter, salt, and icing sugar. Add egg, then sift in flour and cocoa powder. Mix until just combined. Chill the dough, roll it out to 4mm thickness, shape into tart shells using a 6cm half-sphere silicone mold. Chill again, then bake at 325°F for about 12 minutes.
2Heat heavy cream, then pour it over chopped chocolate. Stir until smooth. Pour the filling into the baked tart shells and chill until firm.
3Heat sugar, glucose, cream, and water until boiling. Add soaked gelatin, then pour over chopped chocolate. Blend with a hand blender until smooth. Let the glaze cool slightly, then use it to glaze the chilled tarts.