Turkey Breast Stuffed with Matzo and Fennel

Make stuffing:

• Heat 3 tablespoons oil in a 12-inch heavy skillet over moderately high heat until hot but not smoking, then sauté onion, stirring occasionally, until golden, about 5 minutes. Reduce heat to moderate and add fennel, celery, and 1/2 teaspoon salt, then cook, stirring occasionally, until fennel and celery are golden and tender, 10 to 12 minutes. Transfer vegetables to a bowl to cool.
• Soak raisins in boiling-hot water to cover 5 minutes, then drain well and chop. Add to vegetables.
• Rinse matzo in a colander under hot running water until softened, 15 to 30 seconds. Drain, pressing gently on matzo to extract excess water. Add to vegetables along with egg, parsley, 1/2 teaspoon salt, and 1/2 teaspoon pepper and stir until combined.
• Stir together 1 tablespoon oil, 1/2 teaspoon salt, 1/2 teaspoon pepper, and ground fennel seed in a small bowl.

Bone turkey and remove skin.

Butterfly and flatten turkey:

• Arrange 1 breast half, skinned side down, lengthwise on work surface, with thinner, pointed end nearest you. Starting at top (thicker part), cut breast half lengthwise down middle, but not all the way through to work surface, with a boning knife or a sharp, small knife, stopping about 1 inch from end closest to you. Then, turning knife horizontally, cut turkey breast open on either side like a book jacket, beginning at lengthwise cut, to form 2 flaps. Open flaps, then put butterflied breast between 2 sheets of plastic wrap.
• Pound turkey with flat side of a meat pounder or with a rolling pin until 1/2 inch thick. Butterfly and flatten remaining breast half.

Stuff and roast turkey:

• Put oven rack in middle position and preheat oven to 375°F.
• Remove top sheet of plastic wrap from 1 breast half and pat turkey dry. Arrange with a short side nearest you and season with 1/4 teaspoon salt and 1/4 teaspoon pepper. Mound half of stuffing in center, leaving a 1-inch border on each long side. Fold short end nearest you over stuffing to enclose, gently pressing on filling, then roll to form a cylinder (don’t roll too tight, or filling will slip out of ends). Tie rolled turkey breast crosswise at 1-inch intervals with kitchen string. Season remaining turkey breast half with remaining 1/4 teaspoon each of salt and pepper, then stuff, roll, and tie in same manner.
• Rub fennel oil all over roasts to coat. Heat remaining 2 tablespoons oil in a large heavy flameproof roasting pan straddled across 2 burners on moderately high heat. Add roasts (position 1 roast over each burner) and sear, turning with tongs, until golden brown on all sides, about 6 minutes total. Cover pan tightly with foil and roast turkey in oven until a thermometer inserted diagonally 2 inches into center of each roast (to touch stuffing) registers 165°F, 35 to 40 minutes. Transfer roasts to a cutting board and let stand, loosely covered with foil, 10 minutes before slicing.
• While roasts stand, straddle roasting pan across 2 burners on moderately high heat, then add 1 1/2 cups broth and deglaze by boiling, stirring, and scraping up brown bits, until liquid is reduced to about 1 cup, 2 to 3 minutes. Whisk together remaining 1/4 cup broth and potato starch and whisk into sauce, then boil, whisking, until slightly thickened, 1 to 2 minutes. Pour sauce through a fine-mesh sieve into a sauceboat and skim off any fat. Serve turkey with sauce.