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

Directions

1. 1.

   Place rib roast, fat side up, in heavy roasting pan. 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. Let stand at room temperature 45 minutes before roasting.

2. 2.

   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.

3. 3.

   Melt 2 tablespoons butter with remaining 2 tablespoons oil in large skillet over medium-high heat. Add fresh mushrooms; sauté until browned, about 6 minutes. Add porcini and garlic; stir 1 minute. Remove from heat. 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.

4. 4.

   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.

5. 5.

   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.

6. 6.

   Set roasting pan atop 2 burners over medium-high heat. Add reserved 1 cup porcini soaking liquid, broth, and wine; bring to boil, scraping up any browned bits. 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.

7. 7.

   Garnish roast on platter with fresh rosemary sprigs. Slice roast and serve, passing mushroom sauce separately.