Ingredients
1 (1-inch-thick) boneless beef top loin (strip) steak (½ lb)
1 Tbsp olive oil
1 small garlic clove, finely chopped
1½ Tbsp balsamic vinegar
3 oz mixed baby greens (preferably beet greens; 8 cups)
2 (¼-inch-thick) slices mild blue cheese such as Saga, at room temperature
1 (8-inch) baguette or ciabatta, split
Preparation
Pat steak dry and sprinkle all over with a scant ½ tsp salt and ¼ tsp pepper.
Heat oil in a 10-inch heavy skillet over medium-high heat until it shimmers, then cook steak, turning once, until well browned, 6 to 8 minutes total for medium-rare. Transfer to a cutting board and let stand, uncovered, 10 minutes.
Add garlic to skillet and sauté over medium-high heat 30 seconds. Stir in vinegar, scraping up brown bits, then add greens and sauté, turning with tongs, until wilted, about 1 minute.
Spread cheese onto bread, then sandwich with greens and thin slices of steak.