01 - Preheat oven to 425°F. Arrange beef soup bones on a baking sheet and roast for 30 minutes, turning once, until deeply browned.
02 - Transfer roasted bones to a large stockpot. Add carrots, celery, onion, and garlic.
03 - Pour in cold water to cover contents. Bring to a gentle boil over medium-high heat, skimming off any foam that forms.
04 - Incorporate bay leaves, peppercorns, parsley, thyme if using, and salt.
05 - Reduce heat to low and simmer uncovered for 3.5 hours, occasionally skimming fat and foam.
06 - Remove from heat and carefully strain through a fine-mesh sieve into a large bowl, discarding solids.
07 - Taste and adjust salt as needed. Cool the broth, refrigerate, and skim any solidified fat before serving.
08 - Serve hot as a clear broth or use as a base for other dishes.