Directions:

1. Preheat oven to 350°F. Place potatoes in a large pot. Add water to cover; bring to a boil over high. Add a generous pinch of salt; reduce heat to medium, and simmer until potatoes are tender when pierced using a knife, about 15 minutes. Drain; rinse potatoes under cold water to cool. Drain and pat dry. Cut potatoes into quarters; set aside.
2. Bring cider to a boil in a medium saucepan over medium. Cook, undisturbed, until reduced by half, 5 to 6 minutes. Add cream, and bring to a boil over medium. Cook, stirring occasionally, until reduced by half and cream thickly coats the back of a spoon, 8 to 10 minutes. Stir in 1/2 teaspoon salt. Remove from heat; cover and keep warm.
3. Heat 1 tablespoon oil in a large ovenproof skillet over medium-high. Sprinkle salmon evenly with 1 teaspoon salt. Place salmon, skin side down, in skillet. Cook, undisturbed, until skin is crispy and golden brown, about 5 minutes. Reduce heat to medium; add butter, and baste until top of salmon is no longer translucent, about 1 minute. Transfer skillet to preheated oven; bake until fish is just cooked through and a thermometer inserted into thickest portion of salmon registers 125°F for medium, about 6 minutes.
4. Meanwhile, heat remaining 2 tablespoons oil in a large nonstick skillet over medium-high. Add potatoes, cut side down; cook, undisturbed, until golden brown on 1 side, about 3 minutes. Add remaining 1/2 teaspoon salt; toss potatoes, and cook, stirring occasionally, until golden brown and crisp, 6 to 8 minutes. Remove from heat, and stir in spinach until just wilted, 1 minute. Serve salmon with potatoes and spinach and reserved cider cream sauce.