Savory Slow Cooker Lamb Shanks

2 tablespoons olive oil
4  lamb shanks
1 cup Pinot Noir or Burgundy, or other dry red wine
3 tablespoons grainy Dijon mustard
1 teaspoon balsamic vinegar
1 1/2 teaspoons salt
1/2 teaspoon black pepper
1 heaping tablespoon fresh chopped rosemary, or about 1 1/2 teaspoon dried rosemary
1 tablespoon chopped parsley, or 1 teaspoon dried parsley flakes
4 large cloves garlic, finely minced
16 ounces sliced mushrooms
1 large carrot, diced
12 to 16 ounces small white onions, peeled, or 2 medium onions, cut in wedges

*To peel the onions, drop in boiling water and boil for 3 minutes. Transfer to cold water. Cut off root end and slip off skins. Frozen small white onions may be used.
In a large skillet over medium-high heat, heat the olive oil. Cook the lamb shanks in the hot oil, turning frequently, until browned on all sides. Place the browned lamb shanks in a 5 to 7-quart slow cooker. Add the peeled onions or onion wedges to the slow cooker.

Meanwhile, combine the wine with mustard, vinegar, salt, pepper, rosemary, parsley, and garlic; set aside.
To the hot skillet, add mushrooms and carrots. Cook the mushrooms and carrots for about 5 minutes, stirring constantly. Spoon the vegetables over the lamb shanks. Pour the wine mixture into the skillet, scraping up the browned bits with a spatula. Bring to a simmer; pour over the lamb shanks in the slow cooker.
Cover and cook on HIGH for 2 hours. Reduce heat to LOW and cook for 6 to 8 hours longer.