Beef bones, as many as will fit into your slow cooker. I used a combination of soup bones, marrow bones, and bones from previously roasted prime rib, etc.
2 tablespoons white vinegar or lemon juice
1. Heat oven to 350*F. Spread bones out on baking sheet and roast until browned.
2. Transfer bones to slow cooker and add water up to one inch from top. Add vinegar.
3. Cover and cook on LOW for at least 24 hours and as many as 72. Check occasionally to skim off any scum that has risen to the top and to add more water as necessary.
4. Cool broth to room temperature, remove large chunks of bone or meat, then strain through wire mesh strainer. You can line this with a clean kitchen towel if you’d like for better straining.
5. Cool broth in refrigerator then skim fat off top. You can use this fat for other things if you’d like.
6. At this point you can boil it to condense it if you’d like. Otherwise store it in small ziptop bags, 1/2-1 cup of broth per bag. Freeze flat and stack for later use.
This method is mainly from Food Renegade but I did a lot of googling and reading of other recipes as well. I’ve made this a few times and it’s lovely. I like to condense it and then put 1/2 cup in each of my freezer bags. I reconstitute it with 1/2 cup water to get 1 cup of broth. I haven’t bought beef broth in months!
Only make this if you're okay with making your entire home smell like cow. Preferably not before you have any veg*n company!