Chop the onion with a little black pepper, then add the ground lamb, lamb fat, ground beef, salt, black pepper, and coriander. Process everything together in a food processor until well combined.

Transfer the mixture to a bowl, add the vinegar and oil, and knead by hand. Let it marinate in the refrigerator for 1 to 2 hours.

Shape the mixture onto wooden skewers.

Place the skewers on the oven rack or a grill rack, with a baking pan filled with a little water underneath to create steam and keep the kofta moist. The water will also catch the fat drippings so they don't burn.

Broil in the oven directly under the broiler, turning the skewers occasionally until browned on all sides and cooked through.

You can also bake them directly in a baking pan, but using a rack is better for draining the fat.

Serve hot with a side of tahini sauce.