In a large casserole dish over medium-high heat, fry the chorizo in the butter and oil for 1 minute. Transfer the chorizo onto a plate and set aside. Add the rabbit pieces and sear on all sides. Add the chili flakes and the chestnuts and give everything a good stir. Cook for 1 minute. 

Pour in the chicken stock. Season with salt and pepper. Bring to a boil then reduce the heat and simmer until the rabbit is tender, around 1 hour. 

Remove the rabbit pieces and keep warm in dish covered with aluminum foil. Strain the sauce through a sieve into a clean saucepan. Add the sugar, cocoa powder, spices, mandarin rind, soy sauce and mandarin juice to the saucepan. Cook until reduced slightly and add some water if too dry. Add the grated parmesan and the cooked chorizo. Taste for seasoning and adjust accordingly. 

Arrange the rabbit on a serving platter, cover with the sauce and sprinkle with more grated parmesan, few mandarin rinds or a scatter of pomegranate seeds.