FOR RADICCHIO: In a large nonstick skillet, heat oil over medium-high heat until hot but not smoking. Add radicchio, shallot and garlic; cook, stirring occasionally, until radicchio is wilted, about 3 minutes. Remove pan from heat, add cheese and stir to combine. Transfer mixture to a bowl; remove and discard garlic. Wipe out skillet.

FOR STEAK: On a cutting board, spread peppercorns in a single layer. Using underside of a small heavy skillet, firmly press peppercorns in a rocking motion to coarsely crush. Rub peppercorns into both sides of steaks, then season with salt.

Using same skillet, heat 1 tablespoon oil and 1 tablespoon butter over high heat. Cook 1 steak, turning once, about 7 minutes total for medium rare. Transfer to a cutting board. Wipe out skillet and repeat with remaining steak. Let steaks rest 10 minutes, then slice. Serve with radicchio.