Braised Brussels Sprouts with Mustard Butter

1 pound small, firm, bright green Brussels sprouts
1/2 teaspoon salt
1/2 cup water
2 tablespoons melted unsalted butter or margarine
2 tablespoons Dijon mustard
Salt and freshly ground black pepper
1 Check each head, peel off any loose or discolored leaves. Using a paring knife, cut an X through the core end of each head.
2 Bring sprouts, water and salt to a boil in a 2-quart saucepan over medium-high heat. Lower heat, cover and simmer. Shake pan once or twice during braising to redistribute sprouts.
3 Cook until just tender 8 to 10 minutes. Test by piercing with a knife tip. Drain well.
4 Melt butter in a large skillet of medium heat. Whisk in mustard until smooth. Cook , stirring constantly until smooth and creamy, about 30 seconds.
5 Add sprouts to skillet, coating well with the butter mixture. Season to taste with salt and pepper and serve. Serves 3 to 4.