Heat the oven to 450°F with a rack in the middle position. Put the tahini into a small bowl. Gradually whisk in the boiling water, followed by the yogurt, lemon juice and ½ teaspoon salt. Measure 2 tablespoons of the tahini sauce into another small bowl to use for brushing; reserve the remainder for serving.

In a 9-inch deep-dish pie plate, toss the potatoes with the oil and ½ teaspoon salt. Shingle the slices in the pie plate in concentric circles. Scatter on the sliced onion and pour in ¼ cup water. Cover tightly with foil and bake for 30 minutes.

Remove the foil and bake until a skewer inserted into the potatoes meets no resistance, about another 10 minutes. Remove from the oven; leave the oven on.

In a food processor, combine the chopped onion, the garlic, parsley and jalapeño. Process until finely chopped, scraping the bowl once or twice, about 1 minute. Add the ghee and pulse until combined, 8 to 10 pulses. Transfer to a medium bowl and add the beef, baharat, 1½ teaspoons salt and 1 teaspoon pepper. Using your hands, mix until well combined. Lightly moisten your hands to prevent sticking, then shape the mixture into nine 3-inch cigars (about ¼ cup each) and place them, evenly spaced, on top of the potato-onion mixture.

Bake until the kefta begin to brown and release some juices, 10 to 12 minutes. Remove the pie plate from the oven and brush the kefta with the 2 tablespoons reserved tahini sauce. Return to the oven and bake until the kefta are nicely browned and the centers reach 160°F, another 10 to 12 minutes.

Sprinkle with chopped parsley. Serve with the tahini sauce, lemon wedges and pita.