In a roasting pan season lamb with salt and arrange rib sides down. Roast lamb in middle of oven until a thermometer inserted 2 inches into center of a rack registers 130°F, about 25 minutes, for medium-rare.
While lamb is roasting, mince shallot and with flat side of a large knife crush peppercorns. In a small saucepan cook shallot in 1 tablespoon butter over moderate heat, stirring occasionally, until softened. Add peppercorns and wine and simmer until liquid is reduced to about 1/3 cup.
Transfer lamb to a cutting board and let stand 10 minutes. Skim fat from roasting pan and add red-wine mixture to pan, stirring and scraping up any browned bits. In saucepan simmer sauce until reduced to about 1/4 cup. Whisk in remaining 3 tablespoons butter until incorporated and season sauce with salt if necessary.
Cut lamb into individual chops and pour sauce over them.