Step by step recipe:

1. 2 min.
   Prepare 1 sheet gelatin.
   
   Sieve 125 g chestnut flour and 125 g flour together into a food-mixer bowl.
2. 5 min.
   Add 100 g butter, 100 g caster sugar and 1 egg.
3. 5 min.
   Knead until smoothly mixed.
4. 2 hours
   Gather the pastry into a flat cake, wrap in plastic film and refrigerate for at least 2 hours (it is easy to make this pastry the day before you want to use it).
5. 10 min.
   After this resting time, roll out the pastry and line the tart tins or moulds.
6. 20 min.
   Bake the tart cases "blind".
7. 10 min.
   Squeeze 4 clementines and collect 50 à 60 ml of juice.
   
   Add 50 g caster sugar and melt the sugar over low heat.
   
   Be careful not to let it boil; the clementine juice should be just hot, around 122°F (50°C). Use a thermometer to be sure.
   
   Add the gelatin and mix in thoroughly.
8. 10 min.
   Put the pan to cool by standing it in cold water. Stir from time to time with a whisk.
9. 10 min.
   Melt 75 g white chocolate in a bain-marie.
10. 5 min.
    Use a brush to coat each pastry case with a thin layer of white chocolate.
11. 
    This will keep the pastry crisp by stopping the clementine jelly soaking into it. The white chocolate will barely affect the flavour, if at all.
12. 5 min.
    To finish, fill the tarts with the clementine jelly and leave to set in the fridge.