If your bones are raw, roast in the oven at 200 degrees for 25 minutes.
Put all ingredients in a slow cooker and fill with water.
Simmer for at least 24 hours. You can keep this simmering all week, topping up with more water as required although it tastes best in the first 24 - 48 hours.
Once cooked through, you can strain and store in a plastic jug in the fridge, or otherwise pour into silicone muffin trays and freeze for future use.
Notes
I have not included nutritional information for this recipe, because you are not consuming the vegetables and only the broth. It is generally 70 calories per cup, with 4grams fat, 4 grams protein and no carbs.
Try this with whatever bones you have! I keep my roast chicken bones in the freezer until I have enough to make broth, rather than wasting them because there's not enough.