Stuffed Onions with Spiced Lamb and Pomegranate

Fill a medium pot with enough water to cover the onions and bring to a boil. Add whole onions, return to a boil, and cook until tender, 20 to 25 minutes. Using a slotted spoon, remove onions to a colander, drain, and let stand until cool enough to handle. Cut a 1/2-inch wedge from the outside to the core of each onion, then carefully peel 5 outer layers from each onion and reserve; chop the onion wedges and core, and reserve separately.
In a medium skillet, heat the oil over medium-high. Add the chopped onion and cook, stirring, until golden, 4 to 5 minutes. Add the lamb, anchovies, salt, and pepper and cook, breaking meat up with a wooden spoon, until lamb is no longer pink, 5 to 6 minutes. Add the rice and cook, stirring, until translucent, 2 to 3 minutes. Add the spices and 1 cup broth; cook, stirring, until evaporated, 4 to 5 minutes. Transfer lamb mixture to a rimmed baking sheet and cool slightly; cover and refrigerate for 30 minutes. Remove from the refrigerator, transfer to a bowl, and add parsley, cilantro, and 1 tablespoon pomegranate molasses.
Preheat the oven to 250°F. In a small bowl, whisk together the remaining broth and pomegranate molasses with the tomato paste. Wrap one onion layer around about 2 to 3 tablespoons filling and arrange seam-side down in a 2-quart shallow baking dish. Repeat with remaining onion layers and filling.
Pour liquid over stuffed onions, cover with foil, and roast until tender and some of the liquid is absorbed, 2 hours (you can roast for up to 3 additional hours for softer, more savory onions). Remove from oven and uncover. Preheat broiler and broil until golden brown, 1 to 2 minutes. Let cool for 10 minutes. To serve, drizzle with oil, and garnish with pomegranate seeds, parsley, and cilantro.