Preheat oven to 450°F.Meanwhile, place pork on cutting board, fat side down. With sharp boning or carving knife, cut down along one long side of loin, about 1/2 inch from edge, stopping 1/2 inch from cutting board. Turn knife parallel to cutting board and cut inward 1/2 inch above cutting board, unrolling roast like a carpet. Continue until loin is one long flat piece, about 1/2 inch thick.
Arrange prosciutto and lemon slices evenly over pork. Sprinkle with panko, chives, 1/2 teaspoon salt, and 1/2 teaspoon pepper. Beginning at end that was the interior, roll roast up and tie with kitchen twine at 1 to 1 1/2-inch intervals. Sprinkle all sides with 1 teaspoon salt and 1/2 teaspoon pepper. Arrange pork fat side up in roasting pan and roast 15 minutes.
Reduce oven to 325°F and continue roasting until instant-read thermometer registers 140°F when inserted into thickest part, about 45 minutes longer. Transfer pork to cutting board and let rest 15 minutes.
Meanwhile, place roasting pan on stove top over medium-high heat. Add broth and wine, bring to boil, and cook, scraping up any browned bits, until mixture is reduced to 1 cup, about 8 minutes. Stir in butter. Add cornstarch mixture, stirring until sauce thickens. Remove from heat, strain if desired, and season with salt and pepper.
Remove twine and slice pork crosswise. Serve with sauce.Copyright Jill Silverman Hough. All rights reserved. www.jillhough.com.