How to Make It
Place potatoes in a pot, cover with water and add 1 tsp. salt. Bring to a boil over high heat, reduce heat to medium-low and simmer until potatoes are tender, about 15 minutes. Drain; mash with butter until smooth. Set aside to cool.
Stir salmon, dill, parsley and scallions into potato mixture. Taste; add additional salt and pepper, if desired. Beat 1 egg; stir into potato mixture. Cover and chill for at least 30 minutes.
Divide mixture into 6 pieces; shape into disks. Beat remaining egg. Place flour and bread crumbs in shallow bowls. Coat a disk with flour, dusting off excess, dip in egg, then dip into bread crumbs; pat to adhere. Repeat with remaining disks. (Cakes may be kept covered and chilled for up to 2 days.)
Warm oil in a large skillet over medium-low heat. Working in batches, fry cakes until heated through, 7 to 8 minutes per side.