1. Boil the potatoes in salted water over medium heat about 20 minutes or until very tender. Drain well, return to the pan, and mash.
2. Meanwhile, place the salmon in a frying pan and cover with cold water. Add the onion, peppercorns, and bay leaves. Bring to a boil, then simmer for 5 minutes. Remove from the heat, drain in a colander, and let cool completely, about 20 minutes.
3. Flake the salmon into a large bowl. Add the mashed potatoes, scallions, dill, horseradish, lemon zest and juice, and cayenne and mix well. Season with salt and pepper. Shape into 12 round cakes. If you have time, refrigerate 1 hour before cooking.
4. Process the bread crumbs and chives in a food processor until well combined. Put the flour, eggs, and bread crumbs in shallow dishes. Coat the salmon cakes in flour, then egg, then the herbed bread crumbs.
5. Heat the oil in a frying pan over medium heat. In batches, add the salmon cakes and cook for about 3 minutes on each side, or until crisp and golden brown. Transfer to paper towels to drain. Serve hot, with the lemon wedges.