Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Wash and dry all produce. Place 1 TBSP butter (2 TBSP for 4) in a small bowl; bring to room temperature. Peel and dice potatoes into ½-inch pieces (for speedier spud prep, skip the peeling). Mince or grate garlic. Finely chop parsley leaves and stems.

Toss potatoes on one side of a baking sheet with a drizzle of oil and a pinch of salt and pepper. (For 4 servings, spread potatoes out across entire baking sheet.) Roast on top rack until lightly browned, 10-12 minutes (we’ll add green beans then).

Once potatoes are lightly browned, remove sheet from oven and toss green beans on opposite side with a drizzle of oil, salt, pepper, and garlic. (For 4 servings, leave potatoes roasting and toss green beans on a second sheet; roast on middle rack.) Continue roasting until veggies are browned and tender, 12-15 minutes more.

Once green beans are in the oven, pat steak dry with paper towels and season all over with salt and pepper. Heat a drizzle of oil in a large pan over medium-high heat. Add steak and cook to desired doneness, 3-6 minutes per side. Transfer to a cutting board; let rest 5 minutes.

To bowl with softened butter, stir in 1 tsp mustard (2 tsp for 4 servings; we sent more) and a pinch of parsley. Season with salt and pepper.

Slice steak against the grain; divide between plates. Top steak with herb butter. Serve with green beans and potatoes on the side. Garnish with remaining parsley.