Wash bones in water to get rid of excess blood, till the water is clear, then put into a pot
Add the celery, thyme, parsley, garlic, carrots, onions, bay leaves, coriander seeds, and black peppercorns
Bring to the boil and skim off any impurities/foam and discard
Put the lid on and into a preheated oven at 90c and leave overnight
In the morning, strain the stock through a muslin and discard the veg and bones
Place into the fridge again overnight or until it has cooled, solidified and you can see the fat layer on the top
Remove the fat and keep (you can use it for frying etc)
Put all the stock back into a pot and bring to the boil again, removing any further impurities that arise
You can reduce it a little at this stage if you wish to make it more gelatinous
Then decant into 500ml portions or stock cubes and freeze till ready
