HEAT THE BUTTER OR OIL in a wide pot, add the vegetables, lentils, herbs, garlic, salt, nutritional yeast, if using, and half cup water, and stew over medium-low heat for 15 to 20 minutes. Pour in the 8 cups of cold water and bring to a boil; then simmer, partially covered, for 30 to 40 minutes. Pour the stock through a sieve and press out as much of the liquid as possible. Use it as is, or reduce it further for a richer flavor. Taste and season with more salt, if needed. Makes 4 to 6 Cups