Preheat oven to 180°C/360 °F.
Prep the vegetables: Massage the sliced onions with salt, pepper and all spice. Peel, and chop all vegetables and set them aside.
Season the beef: Sprinkle salt, pepper over the meat slices and massage them well so the seasoning penetrates the beef slices. Dry them with kitchen paper to remove excess moisture.
Sear the beef: Add 2 tablespoons of ghee to a hot skillet over medium-high heat. Add the garlic and one rosemary branch to infuse the ghee. Once the ghee is sizzling, add the meat, three slices of meat at a time, to brown each side. Once nicely browned, remove the meat, the rosemary leaves, and the whole garlic and set them aside warm in a dish.
Sauté the vegetables: In the same hot pan, add the onions, potatoes, colored pepper and tomatoes, and the red tomato paste. Stir everything over high heat for 1 minute. Turn off the heat.
Assemble the dish: Line a sheet pan with aluminum foil topped with a layer of parchment paper. Arrange the vegetables and then top them with the meat. Add the rosemary branch if it hasn’t turned black. Cover the dish with another layer of parchment topped with a layer of foil and tuck the ends of the foil well under the edges of the sheet pan.
Cook Waraket Lahma: Place the sheet pan undisturbed in the oven for 1 hour.
Garnish & Serve: Remove the sheet pan, and with a sharp knife, tear the foil and parchment. Sprinkle the dish with fresh parsley leaves. Taste and adjust the seasoning. Serve it hot next to vermicelli rice.