Rinse salmon; pat dry. In a 10- to 11-inch frying pan over high heat, melt butter. Lay salmon, flesh down, in pan and brown lightly, about 2 minutes. Turn over with a wide spatula and brown skin lightly, about 2 minutes. Lift fish out and set on a plate.
To pan add garlic, onions, and tomato. Stir until juices evaporate, about 2 minutes. Add paprika; stir. Add coconut milk; mix well. Set fish, skin down, in sauce. Cover pan and simmer over medium heat until salmon is opaque but still moist-looking in center of thickest part (cut to test), 5 to 7 minutes, stirring sauce around fish occasionally.
With spatula, transfer fish to a platter; keep warm. Add sour cream to pan and stir over high heat until sauce is boiling. Stir in 2 tablespoons cilantro and pour sauce over fish. Sprinkle with remaining cilantro. Serve fish and sauce over rice. Season to taste with salt and pepper.