Place the beans in a large bowl and cover with 3 to 4 inches of cold water. Soak at least 8 hours or preferably overnight. Drain and rinse the beans. Set aside.

Heat the vegetable oil in a large pot or Dutch oven over medium-high heat for 2 to 3 minutes. Add the bones and sear until nicely browned on all sides, 10 to 12 minutes. Add the 12 cups of water and bring to a boil. Reduce the heat to medium-low and simmer for 1 hour, periodically skimming off any foam that rises to the top.

Whisk together the tomato paste and the remaining ½ cup of water (to thin it out) and stir it into the pot. Add the soaked beans, the cilantro bundle, onion, garlic head, and hawaij. Bring to a boil, then reduce the heat to medium-low to maintain a gentle simmer. Cover and cook until the beans are soft, about 1 to 1½ hours. Remove the lid and season with the salt. Continue to cook until the soup has reduced and thickened slightly, 1 to 1½ hours more. (If you’re in no hurry, let it simmer away over very low heat for up to 4 hours, and it will be even better).