Most vegetable broths use onion, celery and carrot as the base, but when making your own (and it really is so easy to do), you can use all kinds of kitchen scraps for flavor like carrot peel, mushroom stems, green onion ends, shallot and onion skin, and even the stems of your favorite herbs.
Keep in mind that all scraps should be clean and avoid things like cabbage, broccoli and Brussels sprouts because these can leave a bitter taste in a broth. Start with a table spoon of olive oil in a large stock pot over medium heat; add five cloves of minced garlic, two large onions chopped, three ribs of celery chopped, and three carrots chopped. Cook until softened, and then add eight cups of water, your veggie scraps, and herbs to taste. Reduce heat and simmer for forty five minutes. Pour the mixture through a fine mesh strainer and discard or compost the solids. Store your stock in air-tight bags in your freezer so you have stock anytime a recipe calls for it.