Season the fish on both sides with salt and cayenne. In a large nonstick skillet, melt the remaining 1 tablespoon of butter over moderately high heat. Add the fish, skin side up, and cook until golden brown, about 5 minutes. Turn the fish and cook for 1 minute longer, or until just cooked through. Turn the fish again and spoon the soybean crust on top of each fillet, pressing lightly to adhere.