Meanwhile, heat the oil in a large cast-iron skillet until shimmering. Dredge the skin side of the salmon in flour, tapping off any excess. Add the salmon to the skillet, skin side down, and season with salt and pepper. Cook over moderately low heat until the skin is just browned and the flesh near the skin turns opaque, about 5 minutes. Transfer the skillet to the oven and roast the salmon for about 4 minutes, or until barely cooked through. Transfer to a large plate, skin side up, and let rest for about 5 minutes.