1. Pat steak tips dry with paper towels and season with salt and pepper. Heat 1 tablespoon oil in large skillet over medium-high heat until just smoking. Add meat and cook until well browned all over, 6 to 8 minutes. Transfer to serving platter and tent with foil.

2. Heat remaining oil in empty skillet until shimmering. Cook mushrooms, shallots, and ? teaspoon salt, covered, until vegetables have softened, about 3 minutes. Stir in broth, brandy, and thyme and simmer until reduced by half, about 7 minutes. Off heat, stir in sour cream, mustard, and any accumulated steak juices. Season with salt and pepper. Pour sauce over meat. Serve.