Flat-iron steak is a relatively inexpensive cut with great flavor and lots of marbling. It usually comes in one large piece that can be grilled whole like a flank or cut into individual steaks, as it's done here.
Season steaks with salt and let sit at room temperature 30 minutes. Meanwhile, place peppercorns in a plastic bag and coarsely crack with a meat mallet or rolling pin. Transfer peppercorns to a plate. Lightly pat steaks dry and coat both sides of each steak with peppercorns, pressing to adhere.
Heat a medium skillet, preferably cast-iron, over medium-high. Swirl in oil and cook steaks, turning once, until internal temperature reads 135 degrees (for medium-rare), 6 to 8 minutes total. Transfer to a plate and tent with foil.
Discard fat from pan. Add butter and shallots and cook, stirring often, until shallots soften and begin to brown, 1 to 2 minutes. Carefully add cognac and cook, scraping up any bits from the bottom of pan, until almost evaporated, 3 minutes. Add Worcestershire and stock and simmer until reduced by half (to about 1/3 cup), 4 to 5 minutes. Add cream and cook until heated through and thickened slightly, about 1 minute more. Slice steaks against the grain, divide between two plates, and top with sauce.