• Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce. • Dice potatoes into 1⁄2-inch pieces. Mince chives. Cut broccoli florets into bite-size pieces if necessary.

• Place potatoes in a large pot with enough salted water to cover by 2 inches. Bring to a boil and cook until very tender, 15-20 minutes. Reserve 1⁄2 cup potato cooking liquid, then drain. • Return potatoes to pot and add sour cream, half the chives, and 1 TBSP butter (2 TBSP for 4 servings). Mash, adding splashes of reserved cooking liquid as needed, until smooth and creamy. Season with salt and pepper. Cover to keep warm.

• While potatoes cook, toss broccoli on a baking sheet with a large drizzle of olive oil, salt, and pepper. • Roast on top rack, tossing halfway through, until browned and slightly crispy, 15-20 minutes.

• Meanwhile, pat beef* dry with paper towels; season all over with salt and pepper. Heat a drizzle of oil in a large pan over medium-high heat. Add beef and cook until a crust begins to form, 4-7 minutes per side. • Remove from heat; transfer beef to a plate to rest. Wipe out pan.

• Add demi-glace, half the vinegar (all for 4 servings), and 1⁄4 cup water (1⁄3 cup for 4) to pan used for beef over medium-high heat. Bring to a simmer and cook until thickened, 2-3 minutes. • Remove from heat and stir in 1 TBSP butter (2 TBSP for 4) until melted. Season with salt and pepper.

• Divide beef, broccoli, and mashed potatoes between plates. Drizzle beef with sauce. Garnish with remaining chives and serve.