- 1 (4-rib) prime rib roast with ribs (sometimes called standing rib roast; 9 to 10 lb)
- 1/2 oz (2 tablespoons) dried porcini mushrooms, ground to a powder in a blender
- 1 tablespoon kosher salt
- 3/4 teaspoon black pepper
- 2 small onions (1 left unpeeled and halved lengthwise, and 1 peeled and chopped)
- 3/4 stick (6 tablespoons) unsalted butter
- 2/3 cup chopped shallots (about 3 large)
- 1 carrot, finely chopped
- 1 celery rib, finely chopped
- 2 garlic cloves, smashed
- 1 tablespoon tomato paste
- 2 sprigs fresh flat-leaf parsley
- 1 sprig fresh thyme
- 1 Turkish or 1/2 California bay leaf
- 4 black peppercorns
- 1 (750-ml) bottle dry red wine such as a good-quality Côtes du Rhône
- 1/2 oz dried porcini mushrooms
- 2 cups boiling-hot water
- 2/3 cup veal demi-glace
- 1/2 teaspoon salt
- Special equipment: an instant-read thermometer
- Let roast stand at room temperature 1 hour.
- Put oven rack in middle position and preheat oven to 450°F. Trim all but a thin layer of fat from roast, then rub roast all over with porcini powder, salt, and pepper. Transfer to a rack set in a 13- by 9-inch roasting pan. Roast beef 20 minutes, then reduce temperature to 350°F and roast until thermometer inserted into center of meat registers 110°F, 1 1/2 to 2 hours more. Transfer to a large platter and let stand, uncovered, 30 minutes. (Internal temperature of meat will rise to 130°F for medium-rare.)
- Cook halved onion, cut sides down, undisturbed, in 1 tablespoon butter in a 2-quart heavy nonreactive saucepan over moderate heat until browned well, about 4 minutes. Add chopped onion, shallots, carrot, celery, garlic, and 2 tablespoons butter and reduce heat to moderately low, then cook, covered, stirring occasionally, until chopped vegetables are softened, 8 to 10 minutes. Add tomato paste, herbs, bay leaf, peppercorns, and 2 cups wine and boil, uncovered, over moderately high heat until liquid is reduced to about 1/4 cup, 25 to 30 minutes. Pour through a fine-mesh sieve set into another 2-quart heavy saucepan, pressing on and then discarding solids.
- While wine reduces, soak porcini in boiling-hot water (2 cups) in a bowl until softened, about 20 minutes. Drain porcini in a paper-towel-lined sieve set over a bowl and reserve soaking liquid. Rinse porcini and pat dry, then finely chop. Set aside.
- Add porcini-soaking liquid, demi-glace, and remaining 1 3/4 cups wine to reduced liquid in saucepan and boil, uncovered, over moderately high heat, skimming off froth occasionally, until reduced to about 2 cups, 20 to 35 minutes. Stir in reserved porcini, then reduce heat to low and whisk in 1/2 teaspoon salt, any juices from meat accumulated on platter, and remaining 3 tablespoons butter until incorporated.
- Slice roast across the grain and serve with sauce on the side.