Preheat a large cast-iron skillet over medium-high heat. Melt 3 tablespoons butter in skillet. When foam subsides, add scallops in a single layer, being careful not to crowd pan. Season scallops with salt and cook, undisturbed, 2 minutes.
Flip scallops and continue cooking until scallops are firm to the touch, about 1 minute more. Transfer scallops to a serving platter.
Add vinegar, capers, raisins, and parsley to skillet and cook, 30 seconds.
Stir in remaining tablespoon butter and lemon juice. Remove from heat and pour over scallops. Grate nutmeg over scallops and serve immediately.