Place the potatoes in cheesecloth and wring out excess water. You need dry potatoes. In a saute pan, begin making gribenes by caramelizing the onion in the chicken fat. Remove from heat and set aside. In a mixing bowl, stir in the potatoes, caramelized onions, eggs, Matzo Meal, and seasonings together, until a nice, somewhat sticky, mixture is made.
In a skillet over medium heat, start heating the schmaltz for frying. Place large spoonfuls of the potato mixture in the hot oil, pressing down on them to form ¼-½ inch thick patties. Brown on one side, flip, then brown on the other side. Let drain on paper towels. Serve hot with sour cream and/or applesauce.