How to Make It
In a medium saucepan, cover the potatoes with water. Simmer over moderately high heat until tender, about 30 minutes. Drain and let cool. Peel the potatoes and cut them into 1/4-inch dice. Transfer to a large bowl.
Meanwhile, in a large skillet, heat 2 tablespoons of water over moderately high heat. Add the spinach in batches; cook until wilted. Drain, squeeze dry and coarsely chop.
In a small bowl, mix the mayonnaise, jalapeño and chopped dill and season with salt.
Put the salmon in a food processor and pulse a few times, until chopped. Pulse in the cream until incorporated. Add the salmon to the potatoes. Stir in the spinach and onion and season with salt. Form into 12 patties.
In a large nonstick skillet, heat 1/8 inch of oil. Add half of the cakes and fry over high heat until lightly browned on the bottom, 1 minute. Reduce the heat to moderately high and cook until well browned, 2 minutes. Turn and cook for 3 minutes, until browned. Repeat with the remaining cakes; add more oil to the skillet as needed. Garnish the cakes with the dill sprigs and serve with the sauce.