Preheat your oven to 230 C (450 F). Oil a roasting pan and add the marrow bones, onions, carrots, and celery. Roast for 20-30 minutes or until the vegetables are browned, turn the veggies occasionally.

When the veggies are roasted, transfer the bones and veggies to a large stock pot add the water. All the contents should be covered with water.

Now with the roasting pan, pour out any fat and discard that. Add 1/2 cup hot water to the pan and scrape up any bits stuck to the pan, then pour that water into the stock pot.

To the stock pot, now add the tomato paste, peppercorns, and bay leaf. Bring the pot to a simmer and maintain a simmer for 4 to 6 hours. Check the pot once in a while and skim off any foam and fat. Add water as needed to keep the contents covered.

Once simmered, turn off the heat and allow the pot to cool. Remove the bones and discard or for a treat for your dog. Strain the stock and discard what you strained out.

Can be used immediately or stored in the fridge for several days, or even frozen.