Nutrition per serving may change if servings are adjusted.
3 large unpeeled shallots
1½ teaspoons olive oil
1¼ cups port
2 tablespoons butter
2 teaspoons very thinly sliced garlic
3 tablespoons all-purpose flour
1 (14 ounce) can reduced-sodium chicken broth
¼ cup prepared demi-glace (see Tip)
1 teaspoon reduced-sodium soy sauce
⅛ teaspoon freshly ground black pepper
1 ounce dried porcini mushrooms (1 cup)
1½ teaspoons freshly ground black pepper
¾ teaspoon salt
3 (1 to 1¼ pound) racks of lamb, trimmed
Preheat oven to 425°F. In a small baking dish, place shallots; drizzle with oil. Roast, uncovered, about 30 minutes or until tender; cool. Peel and cut away root and stem of each shallot.
Meanwhile, for port sauce, in a small saucepan, bring port to boiling; reduce heat. Simmer, uncovered, for 8 to 9 minutes or until reduced to ⅔ cup; remove from pan. In the same saucepan, melt 1 tablespoon of the butter; add garlic and cook for 1 minute. Stir in flour; cook and stir about 1 minute more or until light golden brown. Gradually whisk in reduced port, the broth, demi-glace, soy sauce and ⅛ teaspoon pepper. Stir shallots into port mixture. Bring to boiling, stirring constantly; reduce heat. Simmer, uncovered, for 2 minutes; strain through a fine sieve. Discard shallots.
In a food processor, combine dried porcini, 1½ teaspoons pepper and salt. Cover and process to a powder.
Arrange oven rack to upper third of oven. Increase oven temperature to 475°F. Sprinkle porcini powder onto all meaty sides of lamb. Arrange lamb on a foil-lined broiler pan, meaty sides up. Roast for 15 to 22 minutes or until an instant-read thermometer inserted in center of lamb registers 135°F.
Transfer lamb to a cutting board. Cover loosely with foil; let stand for 10 minutes. (The temperature of the meat will rise 10 degrees upon standing). Meanwhile, in a small saucepan heat port sauce over medium heat until hot. Cut up remaining 1 tablespoon butter; whisk into hot sauce. To carve racks, cut slices between rib bones. Serve with port sauce.
Tip: Prepared demi-glace may be purchased at specialty food stores.
To make ahead: Prepare through Step 3. Store sauce and porcini powder in covered containers in the refrigerator for up to 24 hours.