To make that nice brown colour the bone marrow has to roast in a very hot oven for 45 minutes at 220 °C .
Halfway through add the onion, carrot and the celery.
Once the ingredients are roasted, transfer them to the pressure cooker and add the Bouquet Garni, and some salt and pepper.
Before adding the water into the pressure cooker, deglaze the roasting pan to make sure all the roasting flavours are added to the stock.
Let the stock cook in the pressure pan for 35 minutes. Once done, remove the ingredients and let it cool completely.
The stock’s temperature has to drop in order for the fat to solidify. If it is winter you can leave the pressure cooker(still sealed) outside, otherwise just keep it in the fridge until is cold enough.
Filter the stock with a percolated coffee filter or a kitchen paper towel, and the stock is ready to be put into their freezing containers or use immediately.
To defrost, microwave the container for 5 minutes, and then use as instructed in your recipe.
Don't miss out, you can eat the marrow on a toasted slice of sourdough bread