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Preheat oven to 425 degrees. Place potatoes on a rimmed baking sheet and toss with 1 tablespoon oil; season with salt. Roast until golden brown and crisp, about 35 minutes, flipping halfway through.
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Meanwhile, spread peppercorns on a large plate. Season steaks with salt, then press into pepper, coating both sides. In a large skillet, heat 1 tablespoon oil and butter over high. In 2 batches, cook steaks until medium rare, about 8 minutes, flipping once. Let rest on a cutting board, 5 to 10 minutes.
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Discard fat from skillet, lightly wipe with a paper towel to remove any loose pepper, and heat over medium. Add wine and cook, stirring and scraping up browned bits with a wooden spoon, until wine is reduced by half, about 2 minutes. Add cream and cook until sauce coats back of spoon, about 4 minutes. Stir in mustard and season with salt.
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Refrigerate 1 steak to use in the Steak Sandwich Wrap. Slice remaining steaks against the grain, divide among four plates, and top with sauce. Serve with potatoes and parsley.