Preparation

Trim excess fat from lamb and remove any membrane. Lightly score flesh with a sharp knife in a diamond pattern, about 1/8 inch deep.

In a small bowl, combine 2 tablespoons kosher salt and 2 teaspoons freshly ground pepper; season lamb all over with salt mixture. Let lamb come to room temperature, about 1 hour.

Preheat oven to 450° with a rack in the lower third. In another bowl, whisk the mustard, garlic, rosemary, soy sauce, and oil until smooth and spread rub evenly over lamb, rubbing it into the scoring. Arrange lamb fat side up on the wire rack in the Hexclad Hybrid Roasting Pan. Pour 1 cup water into the bottom of the pan.

Roast lamb until skin is starting to turn crisp and golden, about 20 minutes. Reduce oven temperature to 325° and continue to roast lamb until a thermometer inserted into thickest part of flesh near the bone reaches 130° for medium-rare, about 1 hour to 1 hour 20 minutes. 

Remove roasting pan from oven and carefully transfer lamb to a serving platter or work surface. Tent with foil and let lamb rest for 20 minutes before slicing. 

Meanwhile, remove the rack from roasting pan and place pan across two burners over medium-high heat. Add flour to pan and cook, stirring until lightly toasted and combined with pan drippings, about 1 minute. Pour in the wine and bring to a boil. Boil until reduced by half, about 2 minutes. Whisk in the broth and continue to boil until gravy is thickened, about 4 minutes more. Carve lamb and serve drizzled with gravy.