1 lb. New potatoes
6 tbsp. unsalted butter
1 clove garlic
¼ c. finely chopped fresh flat-leaf parsley
¼ c. finely chopped fresh chives
2 tbsp. olive oil
1 sirloin steak or London broil
4 plum tomatoes
Place the potatoes in a medium saucepan. Cover with cold water and bring to a boil. Add 1 teaspoon salt, reduce heat, and simmer until tender, 15 to 18 minutes. Drain and return to the pot.
Meanwhile, in a small bowl, combine the butter, garlic, parsley, chives (if using), and 1/4 teaspoon each salt and pepper; set aside.
Heat 1 tablespoon oil in a large skillet over medium-high heat. Season the steak with 1/4 teaspoon each salt and pepper and cook to desired doneness, 4 to 5 minutes per side for medium-rare. Let rest for at least 5 minutes before slicing.
Add the tomatoes to the skillet, drizzle with the remaining tablespoon oil and season with 1/4 teaspoon each salt and pepper. Cook, tossing, just until tender, about 2 minutes; transfer to plates. Add the herb butter to the potatoes and toss to coat. Serve with the tomatoes and steak.