Salmon-and-Mashed-Potato Croquettes

In a saucepan, combine potatoes and enough cold water to fully submerge them. Bring to a boil. Season with 2 teaspoons kosher salt and boil until potatoes are easily pierced with the tip of a knife, 10 to 12 minutes. Drain; let potatoes cool 5 minutes, then press through a ricer or colander and stir until smooth (or mash until smooth). Transfer to a large bowl; let cool completely.

Stir egg yolks, scallions, lemon zest and juice, flour, 2 teaspoons kosher salt, and 1/4 teaspoon pepper into mashed potatoes. Fold in salmon. Form mixture into golf-ball-size rounds, then flatten into 1/2-inch-thick disks. Transfer to a parchment-lined tray and refrigerate until cold, at least 2 hours or, loosely covered, up to 1 day.

Whisk whole eggs in a shallow bowl and season with kosher salt and pepper. Place panko in another shallow bowl and season. Pour a scant 1/2 inch oil into a medium heavy-bottomed skillet, such as cast iron. Heat over medium until oil shimmers and bubbles form instantly around a breadcrumb dropped in (350°F on a deep-fry thermometer). Working in batches, dip croquettes in egg, allowing excess to drip back into bowl, then coat in panko, pressing to adhere.

Fry, flipping once and adjusting heat as needed to maintain a level temperature, until crisp and golden brown, about 5 minutes. Drain on a wire rack set over a rimmed baking sheet, then sprinkle with flaky salt; keep warm in a preheated 200°F oven while frying the rest. Serve warm, with dipping sauces.