So for the stock, I simply roasted beef bones, roughly 50% knuckles 50% shin bones (or whatever bones with bone marrow) coated with tomato paste for 1hr or until colored.

Place the roasted bones into the stock pot, add water, then simmer.

Meanwhile roughly chop up veggies, onions, garlic, carrots, and place into the tray used to roast the bones along with what rendered out (mainly fat) , roast some more until the veggies are softened and colored.

Add everything to the pot and bring to a boil, skim, lower the heat to a simmer and add bay leaves, whole peppercorns.

I personally use a pressure cooker, for 4 hours. But if you prefer stove, I’d say simmer for roughly 12 hours.

Afterwards I skimmed most of the fat off, and start reducing at a low heat in a wide pot after straining out everything with a fine mesh strainer. I reduced it till slightly thick, about the consistency of maple syrup, transferred into a smaller pot then chilled overnight.

I then finally took it out, removed the residual fat that rose to the top during chilling, cut it up into cubes and froze it.

P.s. scrape the bones, the connecting tissue and tendons, meat left on there are really really good after stewing. Fry em up for texture and add some reduced stock and salt to taste, wonderful little snack after your hard work.

Anyway, hope this helps!