Preheat the oven to 425° F. In a large roasting pan, toss together first 5 ingredients. Add in 4 parsley springs and 3 thyme sprigs. Drizzle olive oil over the veggies, and stir to coat. Roast in 425° oven for 30 minutes, stirring occasionally.
Take roasted veggies, and place them in a large stock pot. Add remaining parsley and thyme, peppercorns, bay leaf, leeks, and any other veggie bits. Cover with cold clean filtered water. Cover pan, and bring to a boil. Reduce heat, and simmer with the lid slightly ajar stirring occasionally, for about 60 minutes, or until the veggies are soft.
Strain the broth through a fine mesh sieve to remove all the solids. If you want a super fine clear stock, run the strained broth through a wet coffee filter. Add salt. It may not taste as salty as you’re used to, but it will add good flavor to whatever you’re making. And, if you’re eating it straight, adjust salt and pepper to taste.
Store the broth in the fridge, or if you aren't going to use it right away, store it in the freezer. It can be frozen in ice-cube trays, and then toss those broth cubes in a large plastic bag.
Notes
Amount will vary based on how many veggies you actually throw in the pot, but I usually get about 6-10 cups *Cook’s notes: cremini mushrooms are the little brown mushrooms. I’ve also seen them called Italian mushrooms or baby portabellas. If you can’t find brown mushrooms, white button mushrooms will work just fine. For that matter, so will large portabellas that have been chopped up.