Broth Preparation: Begin with 2-3 lbs (about 0.9-1.4 kg) of beef bones (a mix of marrow, knuckle bones, and meaty ribs is ideal). Roast the bones at 400°F (about 200°C) for 30 minutes to enhance their flavor. Transfer the roasted bones to a large pot, cover with water (about 6 cups or 1.4 liters), and add 2 tablespoons (about 30 ml) of apple cider vinegar to help extract minerals.

Simmering the Broth: Bring the mixture to a boil, then reduce to a simmer. Skim off any scum that rises to the surface. Allow simmering for 12-24 hours, adding water as necessary to keep the bones submerged. Strain the broth to use as the soup base.

Soup Preparation:

Heating the Broth: In a large pot, bring the homemade beef broth to a gentle simmer over medium heat.

Incorporating Beef Tallow: Stir in the beef tallow until it's fully melted and integrated into the broth.

Seasoning: Season with salt and crushed red pepper flakes, adjusting the amounts to suit your taste for saltiness and spiciness.

Final Simmer: Allow the soup to simmer for an additional 10-15 minutes, stirring occasionally, to let the flavors meld together.

Adjustments: Taste and adjust the seasoning if needed. Add more salt or red pepper flakes as desired.

Serving: Once the soup is flavored to your liking and thoroughly heated, remove it from heat and serve hot.