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Preheat your oven to 400.
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Line a baking sheet with foil and place your beef shanks and bones on the foil, sprinkle with salt, and roast at 400 until browned and the marrow is bubbling, about 30 minutes.
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Place the shanks and bones in the bottom of your slow cooker, pour in the apple cider vinegar and add the peppercorns and bay leaves.
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Add the remaining ingredients and cover with cold water.
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Close the lid and cook on low for 24 hours.
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Pour the liquid through a metal strainer and store in glass jars for 3-4 days but you can freeze it for up to a year!