Preheat oven to 300°F.
Pat steaks dry and season both sides with kosher salt.
Coarsely crush peppercorns in a sealed plastic bag with a meat pounder or bottom of a heavy skillet, then press pepper evenly onto both sides of steaks.
Heat a 12-inch heavy skillet over moderately high heat until hot, about 1 minutes, then add oil, swirling skillet, and sauté steaks , turning over once, about 2 minutes per side for medium-rare.
Transfer steaks as cooked to a heatproof platter and keep warm in oven while making sauce.
Pour off fat from skillet, then add shallots and half of butter to pan and cook over lower heat, stirring and scraping up brown bits, until shallots are well-browned all over.
Add Cognac (use caution; it may ignite) and boil, stirring, until liquid is reduced to a glaze, 2 to 3
minutes. Add cream and any meat juices accumulated on platter and boil sauce, stirring occasionally, until reduced by half. Add remaining butter and cook over low heat, swirling skillet, until butter is incorporated. Serve sauce with steaks.