Bone broth has become really popular recently - but you can easily make it at home!
You will need: beef bones (typically knuckle bones), a large slow cooker or roaster, onion skins, water and time
To preserve your broth you can either freeze it in containers or can it. I typically can mine, in which case you will need canning jars with lids and rings, and a pressure canner.
To begin, lay your beef bones out on a baking sheet and heat your oven to 450f. We are going to roast these bones, which will give the broth a lovely roasted flavor and a deep, dark coloring. You can optionally paint your bones with tomato paste or olive oil before roasting them - but I don't. Pop those in, painted or not, for 45 minutes.
As soon as your bones are done roasting, put them in your roaster or large slow cooker. I use my biggest slow cooker because I do not have a roaster. Add in your onion skins - these add depth of flavor and enrich the color as well. Whenever I slice up an onion as I'm cooking, I save the ends and skin in a bag in the freezer for later use in stock. Add water to fill your slow cooker, and you can optionally add bits of garlic or a teaspoon of pepper for flavor. Some folks add vegetable scraps to their beef broth - I save those for my chicken broth and keep the beef broth plain.
Now set your roaster or slow cooker to it's lowest setting, cover, and leave it alone for 48 hours. Check on it now and then and add water if needed to maintain the water level.
After 48 hours of cooking, it's time to strain out the bones and vegetable matter. Don't throw those bones away! We are going to cook them a second time. You can throw away the onion skins though, those we will need to replace. I use a ladle and strainer to get the bones and onion skins strained out of my broth, because it's hard for me to handle the large, hot cooker insert. Do it your way. Once you've got the solids strained out*, fill your canning jars with the hot broth and process in your pressure canner. You have the option of adding a teaspoon or less of salt to each jar - I like to leave my broth unsalted for greater flexibility. Quarts should be processed for 25 minutes and pints for 20 minutes at the appropriate pressure for your altitude (for me, that's 10 pounds).
Put your bones back in the slow cooker and add more onion skins, and garlic and pepper if you liked those. For the second round, I also add 2 tablespoons of apple cider vinegar to help leach the minerals from the bones. This "second round broth" is what you should serve up to sick folks - it contains a lot of minerals and trace elements that boost the immune system. Fill up your slow cooker with water again and cook on low for 4 days. Yes - it seems like forever! But the dark, rich broth you get at the end is worth it! Strain and can just like before.
Use your broth in any recipe that calls for beef stock or beef broth. You can cook rice in it for added flavor, or use it in place of wine in sauce recipes. You can also make it into a nice warm drink when you're feeling under the weather.
(*Some people will strain the broth and then let it cool to skim the fat off. I don't do this. For one thing, the bones I use have little to no fat, so there isn't much in the broth to begin with. For another thing, fat is where your flavor is!)