2 pounds new or other small potatoes
1/4 cup (1/2 stick) butter, melted
2 tablespoons black or mixed peppercorns
1 tablespoon kosher salt
1/4 cup fresh rosemary leaves
1/4 cup olive oil
4- to 5-pound top sirloin roast (also called top butt or spoon roast), trimmed and tied
1/2 cup white wine
1 tablespoon lemon juice
Heat the oven to 400 F.
In a 9-by-14-inch metal (stovetop-safe) roasting pan, combine the potatoes and melted butter. Toss to coat, then arrange in a single layer. Set aside.
In a mini food processor or blender, combine the peppercorns, salt and rosemary. Process until well chopped but not pureed. Transfer to a small bowl and stir in the olive oil. Slather the mixture thickly over the entire roast. Set the roast over the potatoes, then cover with foil and roast for 20 minutes. Remove the foil and continue roasting for another 45 minutes. Reduce the oven to 350 F and roast for another 45 minutes, or until the meat reaches 120 F at the center.
Use tongs to transfer the roast to a serving platter. Cover with foil, then with several kitchen towels to stay warm.
Set the roasting pan with the potatoes over 1 or 2 burners on medium heat on the stovetop. Add the wine and cook, stirring gently, until any browned bits from the bottom of the pan are released and the sauce thickens, about 3 minutes. Stir in the lemon juice. Slice the roast thinly, serve with the potatoes. Spoon the pan sauce over the potatoes.