Combine onion, two teaspoons salt, the pepper, bay leaf, dillseeds, boiling water and vinegar in a deep nine- or ten-inch skillet or saucepan and bring to the boiling point.
Place the salmon on a plate or pie pan and tie in a cheesecloth to keep the fish from breaking apart. Immerse in the boiling mixture, cover, and cook for ten to fifteen minutes, until the fish flakes easily when tested with a fork. Remove from cooking liquid. Strain the liquid and reserve one and one-quarter cups.
Unwrap the fish and place it on a serving dish; keep warm. Sprinkle fish with salt to taste and serve with fresh lemon sauce. Garnish with paprika.