Step 1Combine the creme fraiche and horseradish in a small bowl and mix well. Cover and refrigerate at least one hour or as long as overnight.
Step 2To make the jam, combine the onion in a small saucepan with three-quarters cup of the cider and the vinegar, allspice berries and jalapeno. Bring to a boil over high heat, then reduce the heat to medium and cook, stirring occasionally, for 30 minutes. Remove and discard the allspice. Peel and core the apple, then cut lengthwise into eighths and crosswise into very thin slices. Add the apples to the onion mixture along with the remaining cider. Cook, stirring often, until the mixture is soft, about 30 minutes. Remove the mixture to a bowl and cool to room temperature.
Step 3Peel the potatoes and, using a box grater, shred them into a colander set over a bowl. Press the grated potato to remove excess liquid. Place the grated potato in a clean bowl and add the eggs, salt and pepper and mix thoroughly.
Step 4Heat the oven to 250 degrees. Line a baking sheet with paper towels and set aside.
Step 5Heat 2 tablespoons duck fat in a large skillet over medium heat. Spoon 1 tablespoon of the potato mixture into the hot fat and press to make a pancake about 3 inches across. Repeat with as many pancakes as the pan will contain. Cook about 3 minutes, until golden, then carefully flip each pancake over, press down to compact and cook 3 more minutes, or until the pancakes are crisp and cooked through. Transfer the pancakes to the baking sheet and hold in the oven while frying the remaining pancakes. (Blot any excess grease off.)
Step 6To serve, spoon a tablespoon or so of the apple-onion jam onto each warm pancake and top with a dollop of the creme fraiche.