Balsamic & Dijon Glazed Ham with Roasted Pearl Onions

2 pounds pearl onions
1 cup firmly-packed dark brown sugar
5 tablespoons balsamic vinegar
3 tablespoons Dijon-style mustard
1/4 cup butter, diced
1 teaspoon salt
1/4 teaspoon ground black pepper
1/2 cup water
1 (8- to 10-pound) half ham shank, fully cooked, fat trimmed to 1/2-inch thickness*

* A spiral ham may be substituted, but cooking times will be shorter. Also no need to cut slits.

Cook onions in large pot of boiling salted water 2 minutes; drain. Trim root ends, leaving base intact. Peel. (Can be made 1 day ahead. Cover and refrigerate.)

Preheat oven to 325°F. Line a large roasting pan with aluminum foil.

In a small bowl, combine brown sugar, balsamic vinegar, and Dijon mustard to make the glaze. Transfer onions to 11x7x2-inch glass baking dish. Add 2/3 cup glaze, butter, salt, pepper, and water; toss to coat. Cover with aluminum foil.

Making 1/2-inch-deep slits, score ham with diamond pattern. Place ham in prepared roasting pan and bake 45 minutes. Place onions in oven. Roast ham and onions 25 minutes. Uncover onions, and continue roasting onions and ham an additional 50 minutes. Baste ham with some of glaze. Continue to roast ham and onions until deep brown and glazed, brushing ham with glaze every 10 minutes, about 30 minutes longer. Remove from oven and transfer ham to large platter.

Transfer onion mixture to bowl. Serve ham, passing onion mixture separately.

Makes 12 servings.