To Prepare Sauce: Combine the first 5 ingredients in a small bowl, stirring well. Cover and chill 2 hours.
To Prepare Salmon: Heat white wine, 2 cups water, fresh lemon juice, sliced onion, and 2 dill sprigs in a large skillet to 150 degrees. Cover and simmer 10 minutes. Add fish to wine mixture; cook at 150 degrees for 12 minutes or until desired degree of doneness. Transfer to a serving platter with a slotted spoon. Serve with sauce. Garnish with dill sprigs and lemon wedges, if desired.