Heat a wide heavy pot over medium-high heat with 120g/ 4 oz of a neutral-flavored oil, When the oil begins to smoke, place the bones down in a single layer. You should hear a loud sizzle when placing the bones down. This indicates that the oil was hot enough.
Cook the bones without moving them until golden brown, and delicious for about 10 minutes. Turn the bones and cook for about 10 minutes longer or until evenly colored. If you have trim, add it in after flipping the bones.
For the first deglaze, add 250 ml or 8 oz of water to deglace the pot. Use a wooden spoon, preferably one that is flat, to scrap and lift all the fond. As the water reduces, all the scaped-up fond will dissolve. As the water cooks out, the oil will separate from the water and start sizzling again. This will help continue to brown the bones and help a glaze start forming on the bottom of the pan.
For the second deglaze, add 250 ml or 8 oz chicken stock, scraping up any fond from the bottom of the pan. As the stock reduces, the gelatin from the chicken stock will start to coat the bone and the color of both the bones and stock will deepen. Cook the stock down until a glaze starts to form on the bottom of the pan.
For the third deglaze, add in 125 g or 4.5 oz onion, 90 grams or 3 oz leeks, white and light green parts only, no dark green tops. The vegetables, mostly the onion, will provide the moister for the deglaze. Cook the vegetables over medium heat so that they lightly caramelize.
For the fourth deglaze, add 500 ml or 16 oz each of chicken stock, brown veal stock, and water. Bring this to a simmer, then pull the pan halfway to the burner. This will create a convection simmer and force the impurities off to one side, making it easier to skim.
Once the visible impurities are removed, move the pan back to the center of the burner and cook on a gentle simmer for 45 minutes or until the stock has reduced to the level of the bones, skimming as any impurities float to the top.
Separate the bones and veg from the stock, then double strain this into a smaller pot. Use a swirling motion to help pass the sauce, never forcing the stock through with a ladle. You should have around 500 ml or 16 oz of liquid.
Place this into a smaller container and reduce by half or until nappe which means to coat the back of a spoon, then strain this into a small sauce pot.
