Heat a large pot over medium heat. Once hot, add oil (or water), onion, garlic, carrots, and celery. Add 1/2 tsp each sea salt and black pepper (amount as recipe is written // adjust if altering batch size) and stir to coat. Sauté for about 5 minutes or until softened and slightly browned, stirring frequently.
Add water, greens, parsley, thyme, rosemary, bay leaves, and another 1/2 tsp sea salt and black pepper (amount as recipe is written // adjust if altering batch size) and increase heat to medium high until the mixture comes to a boil. Once boiling, reduce heat to a simmer and add nutritional yeast and tomato paste (add less of both for less intense flavor, or more for bigger more robust flavor!). Stir to combine and loosely cover (with the lid cracked).
Continue cooking for at least 30 minutes, preferably 45 minutes to 1 hour. The flavor will deepen the longer it cooks.
Near the end of cooking, taste and adjust flavor as needed, adding more herbs for herby/earthy flavor, salt for saltiness, pepper for a little spice, or tomato paste or nutritional yeast for "umami" and depth of flavor. In total, I added about 2 tsp sea salt and black pepper (amount as recipe is written // adjust if altering batch size) and all of the suggested amount of nutritional yeast and tomato paste (both of which add depth of flavor and make the broth rich).
Let cool slightly before pouring over a strainer into another pot. Then divide between storage vessels (I prefer glass mason jars). Let cool completely before sealing. Store in the refrigerator up to 5 days or in the freezer up to 1 month (sometimes longer). Perfect for use in soups, recipes, gravy, and more! Recipes listed above.
*If using leftover veggie scraps: either add in addition to the vegetables or slightly scale the vegetables back. They can be added straight from frozen. *Nutrition information is a rough estimate calculated with avocado oil, all of the recommended salt, pepper, tomato paste, and nutritional yeast and with half of the vegetables because they are strained. *You can sub 1 Tbsp dried thyme or rosemary per small handful fresh herb. *Recipe makes ~10 cups broth. *Recipe inspiration from Jennifer's Kitchen.