|Onion||1 Large, peeled, and halved crosswise|
|Bone in beef shank||6 Pound, cut crosswise into 2-inch-thick slices and trimmed of excess fat (Ask Your Butcher To Do This For You)|
|Ground black pepper||To Taste|
|Coarse sea salt/Kosher salt||To Taste|
|Vegetable oil||2 Tablespoon|
|White mushrooms||6 Large, trimmed, cleaned, and halved|
|Celery stalks||4 , trimmed and cut into 2-inch pieces|
|Carrots||3 , peeled, trimmed, and cut into 1-inch pieces|
|Garlic||6 Clove (30 gm), peeled and crushed|
|Flat leaf parsley sprigs||5|
|Coriander seeds||1 Teaspoon, toasted|
1. Heat a griddle or small cast-iron skillet over high heat. Place the onion halves in the pan, cut side down, and cook until blackened (they should be as dark as you can get them). Transfer the onion to a plate and stick 1 whole clove in each half.
2. Season the beef with salt and pepper. Heat the oil in a large nonstick skillet over high heat. Working in batches, sear the beef until well browned on all sides, about 20 minutes per batch. As the pieces of meat are browned, transfer them to a large stockpot.
3. When all the meat is browned and in the stockpot, pour in 6 quarts water, add the remaining ingredients, and bring the liquid to a boil. Lower the heat to a simmer and cook for 2 hours, frequently skimming off the foam and fat that bubble to the surface.
4. Strain the stock through a colander and then pass it through a chinois or fine-mesh sieve. Let cool to room temperature, then cover and refrigerate. (The stock can be kept tightly covered in the refrigerator for up to 4 days or in the freezer for up to 1 month.) When the stock is chilled, the fat will rise to the top. Before reheating the stock, spoon off and discard the fat.