Step by step recipe:

1. 40 min.

   Prepare the tart case

   
   Roll out 300 g Sweetcrust pastry (pâte sablée) to line the tin or mould and bake blind.
2. 5 min.
   While the tart case is cooling, melt 50 g white chocolate in a bain-marie.
3. 5 min.
   When the white choloclate has melted, use a brush to apply a thin, even coat to the bottom of the pastry case and to halfway up the sides.
   
   This is not essential, but it protects the pastry and helps to keep it crisp for longer.
4. 10 min.

   Prepare the chocolate ganache

   
   Put 2 sheets gelatin to soak in a dish of cold water for 10 minutes.
   
   Prepare 300 g Chocolate ganache.
5. 2 min.
   Mix the drained and dried gelatin into the chocolate ganache while it is still hot.
   
   Set aside and keep warm to prevent it setting.
6. 

   Prepare the orange curd

   Prepare 300 g Lime (or lemon) curd, but using oranges instead of lemons...
7. 40 min.
   ...to make orange curd.
   
   Keep warm so that it stays fairly runny.
8. 2 min.

   Fill the tart

   
   Stand the pastry case on the serving plate.
9. 5 min.
   Cut a piece of thin card the same length as the diagonal of the tart.
   
   If you are making a round tart, use the diameter of the tin or mould.
   
   Cover the card with aluminium foil, then wedge it into the tart case, like in the photo.
   
   This is the tricky part: you need to keep the card upright as this is what will stop the two fillings running into each other.
10. 5 min.
    Pour half the chocolate ganache into one half of the tart and half the orange curd into the other.
    
    Wait until the fillings thicken up and begin to set. Refrigerate if possible to speed up this process.
11. 30 min.
    When the fillings are set enough and "pasty" to the touch, pour the remaining fillings into the tart, changing sides (chocolate on top of orange, orange on top of chocolate).
12. 2 min.
    When the second layer is beginning to set (pasty to the touch, like before), gently remove the card.
13. 5 min.
    Make a meringue with 1 egg white and 50 g caster sugar.
14. 2 min.
    Use a forcing bag to pipe a decorative strip that will hide the join between the chocolate and orange fillings.
15. 2 min.
    Give your masterpiece a finishing touch with a quick blast from a torch...
16. 
    ...to brown the meringue and make it more attractive.
17. 
    Your two-coloured orange-chocolate tart is ready.