Rosemary Mustard Sirloin Steak with Garlic Mashed Potatoes and Roasted Brussels Sprouts

This sirloin steak recipe is all about bold, savory flavors and a touch of elegance. The steak is seared to perfection and topped with a luscious pan sauce made with rosemary, Dijon mustard and beef demi-glace. Paired with creamy garlic mashed potatoes and caramelized roasted Brussels sprouts, this meal feels like a special occasion but is simple enough for a weeknight.

The secret to the sauce is the beef demi-glace, which adds deep, rich flavor without hours of simmering. A squeeze of roasted lemon and a sprinkle of chili flakes brighten the Brussels sprouts, balancing the richness of the dish. Serve this impressive dinner to guests or treat yourself to a restaurant-quality meal at home.

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Ingredients

16 ounce Brussels SproutsView ingredient guideLike ingredientDislike ingredient

24 ounce Yukon Gold PotatoesView ingredient guideLike ingredientDislike ingredient

4 clove GarlicView ingredient guideLike ingredientDislike ingredient

1 unit LemonView ingredient guideLike ingredientDislike ingredient

4 tablespoon Sour CreamView ingredient guideLike ingredientDislike ingredient

28 ounce Sirloin SteakView ingredient guideLike ingredientDislike ingredient

0.25 ounce RosemaryView ingredient guideLike ingredientDislike ingredient

2 unit Beef Demi-GlaceView ingredient guideLike ingredientDislike ingredient

4 teaspoon Dijon MustardView ingredient guideLike ingredientDislike ingredient

1 teaspoon Chili FlakesView ingredient guideLike ingredientDislike ingredient

2 teaspoon Vegetable OilView ingredient guideLike ingredientDislike ingredient

2 teaspoon Olive OilView ingredient guideLike ingredientDislike ingredient

4 tablespoon ButterView ingredient guideLike ingredientDislike ingredient

SaltView ingredient guideLike ingredientDislike ingredient

PepperView ingredient guideLike ingredientDislike ingredient

Instructions

1. Adjust rack to top position and preheat oven to 425°F. Wash and dry all produce. Trim and halve Brussels sprouts. Mince or grate 2 garlic cloves; set aside. Zest and halve the lemon. Dice potatoes into ½-inch pieces (no need to peel). Place potatoes in a large pot and cover with salted water. Bring to a boil and cook until tender, about 15 minutes.
2. Drain potatoes. In the same pot, melt 2 tablespoons butter over low heat. Add minced garlic and cook until fragrant, about 30 seconds. Return potatoes to pot and mash until smooth. Stir in sour cream and season with salt and pepper. Keep covered until ready to serve.
3. Meanwhile, in a large bowl, toss Brussels sprouts with a drizzle of olive oil, salt and pepper. Spread on a baking sheet along with one lemon half. Roast on top rack until golden brown, 20-25 minutes.
4. Pat steak dry with paper towels and season generously with salt and pepper. Heat a drizzle of vegetable oil in a large pan over medium-high heat. Add steak and cook to desired doneness, 3-6 minutes per side. Remove steak from pan and let rest. Wipe out the pan.
5. In the same pan, melt 2 tablespoons butter over medium heat. Add remaining 2 garlic cloves and 1 sprig rosemary. Cook, stirring often, until fragrant, about 1 minute. Reduce heat to low. Add beef demi-glace, Dijon mustard and ¼ cup water. Cook, stirring, until combined, 1-2 minutes. Stir in any resting juices from the steak. Remove from heat and season with salt and pepper. Discard garlic and rosemary.
6. Slice rested steak against the grain. Squeeze roasted lemon half over Brussels sprouts and sprinkle with lemon zest and chili flakes to taste. Divide steak, Brussels sprouts and mashed potatoes among plates. Spoon sauce over steak and serve.

Recipe Tips

FAQ

Can I use a different cut of steak?

Yes, you can substitute with ribeye or strip steak. Adjust cooking time as needed.

Can I make the mashed potatoes ahead?

Yes, prepare them up to 2 hours ahead and reheat gently with a splash of milk.

What can I use instead of demi-glace?

You can substitute with beef broth plus a teaspoon of tomato paste, but the flavor will be less rich.