1. To prepare sauce, combine the first 5 ingredients in a small bowl, stirring well. Cover and chill 2 hours.
2. To prepare salmon, heat white wine, 2 cups water, fresh lemon juice, sliced onion, and 2 dill sprigs in a large skillet to 150°. Cover and simmer 10 minutes. Add fish to wine mixture; cook at 150° 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.
Wine note: Poached salmon is naturally rich and meaty. In this dish, it gets a kick from the delicious pungency of dill and mustard. A great wine companion needs to be able to counterbalance all three. For its precise, clean flavors and rush of citrus, I love the King Estate Domaine Pinot Gris from Oregon. The 2007 is about $25. —Karen MacNeil