Coarse or kosher salt and freshly ground pepperto taste
Preheat the oven to 425°F. Heat a heavy, ovenproof skillet over high heat, and add the olive oil.
Brush some olive oil over each piece of salmon, and season with salt and pepper. Add them to the pan skin side down (if relevant). Allow to sear, without moving, in the pan for about 3 minutes. Transfer to the oven and roast for 5 to 8 minutes, until done to your liking (check out this video, it’s so helpful).
While the salmon is cooking, in a small container combine the olive oil, orange juice, lemon juice, tarragon, shallots, Dijon mustard and salt and pepper. Shake to blend well.
Transfer the fish to a serving platter or individual plates. Shake the vinaigrette to remix, then pour it over the fish. Serve hot or warm.