Preheat oven to 425°F. Arrange beef bones, halved onion, carrots, and celery on a rimmed baking sheet. Roast until browned and fragrant, about 30 minutes.

Transfer the roasted bones and vegetables into a large stockpot. Add garlic cloves, bay leaves, and whole black peppercorns.

Sprinkle smoked paprika over the contents. Pour in cold water, covering ingredients by at least 2 inches.

Stir in apple cider vinegar. Bring to a gentle boil, then reduce heat to low. Simmer uncovered for 8–10 hours, skimming foam every hour.

After simmering, remove pot from heat and let cool slightly. Strain the liquid through a fine-mesh sieve into a clean container.

Refrigerate until fat rises and solidifies on top, about 4–6 hours. Skim off the hardened fat layer before use or storage.