To make Roasted Leg of Lamb: Heat oven to 400 degrees. In bowl, whisk olive oil, raspberry balsamic glaze, rosemary and mustard; set aside.
Make small incisions in lamb and insert garlic slices. Rub olive oil mixture over lamb. Sprinkle with salt and pepper. Transfer to roasting pan fitted with rack.
Add onions; pour water into bottom of pan. Roast for 80-90 minutes, or until internal temperature reaches 145 degrees for medium-rare, adding water to pan as needed to avoid scorching and onions drying out.
Transfer lamb to carving board and tent with foil.
To make gravy: Place roasting pan on stovetop over medium-high heat; stir in flour. Whisk in wine; boil 1-2 minutes, or until reduced by half. Whisk in chicken stock and raspberry balsamic glaze.
Add rosemary; bring to boil and simmer 8-10 minutes, or until thickened. Season with salt and pepper. Serve with lamb.