Preheat the oven to 450°F and line a baking sheet with parchment paper.
Trim the celery and carrots, cut the onion in half, and cut the bottoms off the garlic.
Place the bones in a large pot and cover with water. Bring to a boil, then lower the heat to a simmer. Cook for 15 minutes.
Remove the bones from the pot and dry them off. Discard the water.
Place the bones on the prepared baking sheet with the celery, carrots, garlic, and onions. Cover everything with olive oil.
Roast for 30 minutes until the bones are brown and the greens are mostly wilted.
Add all of the veggies and bones into a large stock pot and cover with water.
Add the peppercorns and bay leaves to the pot and set over high heat.
Bring the water to a boil then reduce heat to a simmer. Cover the pot and cook for 4-6 hours.
Strain the vegetables and bone out of the pot carefully over a bowl large enough to hold all the broth.
Season the broth to taste with salt and pepper. Save to use in soups, stews, or other cooking.
