Ingredients:

2 teaspoons canola oil
1 pound flank steak, trimmed
1 tablespoon canola oil
4 large portobello mushrooms, stemmed, halved and thinly sliced
1 large onion, sliced
3/4 teaspoon dried thyme leaves
1/2 teaspoon salt
1/2 teaspoon freshly ground pepper
3 tablespoons all-purpose flour
1 (14.25 ounce) can reduced-sodium beef broth
2 tablespoons cognac or brandy
1 tablespoon red-wine vinegar
1/2 cup reduced-fat sour cream
4 tablespoons chopped fresh chives or parsley, divided

Method:

Heat 2 teaspoons oil in a large skillet over high heat until shimmering but not smoking. Add steak and cook until browned on both sides, 3 to 4 minutes per side. (The meat will be rare, but will continue to cook as it rests.) Transfer to a cutting board and let rest for 5 minutes. Cut lengthwise into 2 long pieces then crosswise, across the grain, into 1/4-inch-thick slices.

Heat the remaining 1 tablespoon oil in the skillet over medium heat. Add mushrooms, onion, thyme, salt and pepper and cook, stirring often, until the vegetables are very tender and lightly browned, 8 to 12 minutes. Sprinkle flour over the vegetables; stir to coat. Stir in broth, cognac (or brandy) and vinegar and bring to a boil, stirring often. Reduce heat to a simmer, and continue cooking, stirring often, until the mixture is thickened, about 3 minutes. Stir in sour cream, chives (or parsley), the sliced steak and any accumulated juices. Bring to a simmer and cook, stirring, until heated through, 1 to 2 minutes more.