Preheat the oven to 160C/140C fan/gas mark 3 or you can use the hob if you prefer. Heat the oil in a heavy based, flameproof casserole dish that has a lid, then add the onions, peppercorns, bay leaves, cloves and cinnamon stick and cook gently for about 10 minutes until the onions have softened. Then add the garlic and cook gently for a further 5 minutes.