Rosemary-and-Pepper Standing Rib Roast with Two-Mushroom Pan Sauce

Ingredients

• 2 tablespoons flour 
• 2 teaspoons pepper black freshly ground
• 4 tablespoons butter divided room temperature ()
• 10 ounces mushrooms fresh cut into 1/4-inch-thick slices
• 1 tablespoon kosher salt 
• 1.5 ounces the following: parmesan rind) dried
• 6.5 teaspoons rosemary dried divided crushed
• 0.8 cup wine dry red
• 2 bunches rosemary leaves fresh (for garnish)
• 4  garlic clove minced
• 1.5 cups beef broth 
• 0.5 cup olive oil 
• 1  prime rib roast with 4 bones)
• 2 cups water boiling

Equipment

• bowl
• frying pan
• oven
• whisk
• sieve
• roasting pan
• kitchen thermometer
• aluminum foil
• measuring cup

Directions

1. Place rib roast, fat side up, in heavy roasting pan.
2. Mix 4 teaspoons crushed rosemary, salt, and pepper in small bowl. Stir in 1/2 cup oil. Rub mixture all over roast. DO AHEAD Can be made 1 day ahead. Cover and chill.
3. Let stand at room temperature 45 minutes before roasting.
4. Combine 2 cups boiling water and porcini; let soak until mushrooms soften, about 20 minutes. Strain soaking liquid through fine strainer set over measuring cup; reserve porcini. If needed, add enough water to soaking liquid to measure 1 cup. Coarsely chop porcini.
5. Melt 2 tablespoons butter with remaining 2 tablespoons oil in large skillet over medium-high heat.
6. Add fresh mushrooms; sauté until browned, about 6 minutes.
7. Add porcini and garlic; stir 1 minute.
8. Remove from heat.
9. Combine flour, remaining 2 tablespoons butter, and remaining 2 1/2 teaspoons crushed rosemary in small bowl; mash with fork to smooth paste. DO AHEAD Porcini soaking liquid, mushroom mixture, and flour-butter mixture can be made 1 day ahead. Cover separately; chill.
10. Place rack in bottom third of oven and preheat to 350°F. Cook roast until instant-read thermometer inserted straight down into top center of roast registers 125°F to 130°F for medium-rare, about 2 hours 30 minutes.
11. Transfer roast to platter; cover loosely with foil and let rest 35 to 40 minutes. Skim any fat from top of pan juices (there will be a small amount of pan drippings); reserve juices in pan.
12. Set roasting pan atop 2 burners over medium-high heat.
13. Add reserved 1 cup porcini soaking liquid, broth, and wine; bring to boil, scraping up any browned bits.
14. Add mushroom mixture, then butter-flour mixture; whisk constantly over medium-high heat until sauce thickens, about 2 minutes. Season sauce to taste with salt and pepper.
15. Garnish roast on platter with fresh rosemary sprigs. Slice roast and serve, passing mushroom sauce separately.