Prick the potatoes a few times with a fork and bake them on a rack in the middle of a preheated 450 degree oven for 1 1/2 hours.
While the potatoes are baking, in a small bowl dissolve the cornstarch in 2 tablespoons of the yogurt and in a saucepan simmer the cornstarch mixture and the remaining yogurt, whisking, for 5 minutes. Stir in the garlic paste, simmer the sauce, whisking, for 2 minutes, and keep it warm, covered. In a skillet cook the walnuts in the oil over moderate heat, stirring, for 1 to 2 minutes, or until they are golden, and transfer them with a slotted spoon to a large bowl. In the oil remaining in the skillet cook the onion, stirring occasionally, until it is golden, add the chuck, and brown the meat, breaking up the lumps.
While the baked potatoes are still warm, halve them lengthwise, scoop out the flesh, leaving crisp shells, and chop coarse the flesh. In the large bowl combine well the walnuts, the chuck mixture, the chopped potato, the cinnamon, the parsley, and salt and pepper to taste, divide the mixture among the potato shells, and top it with some of the sauce. Bake the potatoes on a baking sheet in the 450 degree oven for 10 to 15 minutes, or until the filling is hot, and serve them with the remaining sauce.
Courtesy of Gourmet Magazine