Position oven rack in lowest position and preheat oven to 350°F.

In a medium saucepan, whisk vinegar, sugar, mustard, Worcestershire, and salt. Bring mixture to a simmer over medium-high heat and cook for about 2 minutes, or until it thickens slightly.

Set mustard barbecue sauce aside to cool.

Place carrots, celery, and onion in a 13x9-inch baking dish.

Remove all packaging from ham and pat ham dry.

Run a small sharp knife down the back of ham and, using your fingers, gently separate skin from fat.

Remove and discard skin. Run knife over fat to lightly score it all over.

Place ham in baking dish.

Cover dish tightly with foil and bake for 11/2 to 2 hours, or until ham is warmed through (an instant-read meat thermometer inserted into thickest part of ham will register 110°F).

Increase oven temperature to 400°F.

Using a pastry brush, brush some mustard barbecue sauce all over ham. Return ham to oven uncovered and cook, basting it every 10 minutes with sauce, for 30 to 35 minutes, or until ham is evenly glazed.

Transfer ham to a platter to rest for 15 minutes, tented loosely with foil.

Meanwhile, pour off juices from baking dish into a tall and narrow heatproof container and allow fat to settle to a top. Skim off as much fat as possible and discard fat.

In a serving bowl, whisk equal parts of skimmed juices and remaining sauce.

Carve ham and serve remaining mustard barbecue sauce alongside.

Enjoy!