Holiday Roast With Portabella Sauce

• 4 lbs prime rib roast
• cream of mushroom soup mix, 1 packet
• 2 portabella mushrooms
• 1 cup beef stock
• 2 teaspoons flour
• 1 tablespoon balsamic vinegar or 1 tablespoon red wine vinegar

1. Place roast, fat side up, on rack in roasting pan without lid.
2. Rub mushroom soup mix over surface of roast.
3. Insert meat thermometer into centre of roast, avoiding fat or bone.
4. Roast at 325 degrees for 2 hours.
5. Tent roast with foil and let stand for 10 to 15 minutes on cutting board before carving.
6. Meanwhile, slice mushrooms 1/4 inch thick; cut each slice in half lengthwise.
7. Heat roasting pan over medium-high heat for 1 minute.
8. Pour in beef stock, stirring to scrape up any brown bits.
9. Add mushrooms and simmer 10 minutes.
10. Mix flour with vinegar and whisk into pan.
11. Bring to a boil, whisking constantly until thickened.
12. Season with salt and pepper to taste.
13. Serve roast and sauce with small roasted potatoes and steamed vegetables.

prime, cream of mushroom soup mix, portabella mushrooms, beef stock, flour, balsamic vinegar

Taken from www.food.com/recipe/holiday-roast-with-portabella-sauce-94060 (may not work)