Wash and brush the oranges. Boil them for 30 minutes in plenty of water. Drain.
Halve the oranges and remove their white middles, then weigh them out.
Roughly chop and fry in butter with the brown sugar.
Leave them to caramelize on a low heat, add the sugars and cover with one-third of the passionfruit pulp.
Leave to reduce until almost all the liquid has evaporated.
Cover with another third of the passionfruit pulp and leave to reduce.
In an electric mixer, thoroughly blend the oranges.
Add the starch (which you have mixed in advance with the final third of passion fruit pulp).
Boil for a few minutes, stirring vigorously.