Cream the gluten free flour, salt, and sugar with cold butter in a bowl using your fingers.

Incorporate the water in 3 batches until the dough holds together and forms a ball. Wrap the dough with cling film, then rest in the fridge for at least 30 minutes.

Roll out the crust dough between two parchment papers to prevent it from sticking to the work surface. The ideal thickness is about 3-4 mm (0.16 in).

Cut the dough according to the size of the tart tins. Press the cut dough into the tart tins, then freeze for at least 30 minutes.

Preheat the oven to 180°C (356°F). Bake for 18 to 20 minutes, then let the tart shells cool to room temperature before filling.

Heat the double cream in a saucepan until it comes to a boil.

In a bowl, pour the hot cream onto the chocolate, then mix using a hand blender until smooth and shiny.

If you don't have a hand blender, pour the hot cream in 3 batches over the chocolate while continuously stirring until smooth and shiny.

Fill the tart shells with warm chocolate ganache, then tap a few times to make the filling even.

Sprinkle with cacao nibs on top. Chill for 10 minutes to set before serving.