Preheat the oven to 350˚F.
Place the potatoes in a saucepan and cover with cold water. Season well wth salt. Bring to a boil. Cook at a gentle boil until the potatoes are very tender, about 10-15 minutes. Drain well, then transfer to a large bowl. Using a fork, break up the potatoes until light and fluffy.
Meanwhile, put the salmon on a parchment-lined baking sheet and season with salt and pepper. Bake until medium-rare (it should still be quite pink in the middle), about 12-15 minutes, depending on the thickness of your salmon. Gently flake the salmon, discarding the skin.
Add the flaked salmon to the potatoes, along with the scallions, garlic, ginger, tamari and toasted sesame oil. Season with salt and pepper. Stir with a fork until evenly combined. Form the mixture into ½-cup patties (you should get 8 patties). Do Ahead: The patties can be covered tightly and refrigerated overnight.
In a large nonstick skillet, heat about ¼ inch of oil until shimmering. Pan-fry half of the cakes over medium-high heat until browned and crisp on both sides, about 2-4 minutes per side. Transfer to a paper towel-lined plate and sprinkle with salt. Repeat with the remaining cakes, adjusting the heat as needed. Arrange the cakes on a baking sheet and bake for 15 minutes, or until heated through.
Serve the salmon potato cakes warm from the oven with the Creamy Yogurt Sauce.