Then, I stuff the slow cooker full with 1 lb of mixed greens and stems (any combination of chard, beet greens, kale, spinach, and parsley is fantastic).
Cook it on high for 2 hours (it will take a couple hours for the greens and lid to settle).
After 2 hours, reduce heat to low and cook for 16 more hours (if your slow cooker is like mine, you will need to restart it a couple of times so it doesn’t automatically shut off).
Let it cool on the counter for 2 hours, then remove greens, garlic, onion, and bones.
Chill for at least 6 hours. A layer of fat will float to the top—just scrape it off. Strain solids from broth. After that, your broth is ready to concentrate.
Using the 4 cups of fresh bone broth
Line an 8" glass baking dish with parchment paper; set aside.
In a medium saucepan over medium heat, bring bone broth to a simmer. Continue to simmer for 1 hour, 15 minutes, or until broth has reduced to about 1⁄4 of its original volume and is thick and syrupy. Remove from heat.
Pour reduced broth into prepared baking dish. Refrigerate for 1 hour, or until firm.
4. Remove from baking dish and cut into 16 squares. Freeze until ready to use. To reconstitute, dissolve 1 square in 1⁄4 cup to 1 cup hot water, depending on how you intend to use it.