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

Indulge in a luxurious steakhouse dinner at home with this recipe for Rosemary Mustard Sirloin Steaks. Perfectly seared sirloin is paired with creamy garlic mashed potatoes and caramelized roasted Brussels sprouts, all brought together by a velvety demi-glace sauce infused with rosemary and Dijon mustard.

The secret to this dish’s deep, savory flavor is a ready-made beef demi-glace, which simmers into an intensely rich sauce in minutes. With minimal effort, you can create a meal that tastes like it took hours to prepare-ideal for impressing guests or treating yourself to something special.

Log in to save recipes and build weekly shopping lists.

Ingredients

8 ounce Brussels SproutsView ingredient guideLike ingredientDislike ingredient

12 ounce Yukon Gold PotatoesView ingredient guideLike ingredientDislike ingredient

2 clove GarlicView ingredient guideLike ingredientDislike ingredient

1 unit LemonView ingredient guideLike ingredientDislike ingredient

2 tablespoon Sour CreamView ingredient guideLike ingredientDislike ingredient

14 ounce Sirloin SteakView ingredient guideLike ingredientDislike ingredient

0.25 ounce RosemaryView ingredient guideLike ingredientDislike ingredient

1 unit Beef Demi-GlaceView ingredient guideLike ingredientDislike ingredient

2 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 1 clove garlic (2 cloves for 4 servings). Zest the lemon, then halve it. Dice potatoes into ½-inch pieces (no need to peel). Place potatoes in a large pot with salted water to cover. Boil until tender, about 15 minutes.
2. Drain potatoes. Melt 2 tablespoons butter in the same pot over low heat. Add minced garlic; cook until fragrant, about 30 seconds. Return potatoes to pot; mash with a potato masher until smooth. Stir in sour cream; season with salt and pepper. Keep covered until ready to serve.
3. Meanwhile, toss Brussels sprouts in a large bowl with a drizzle of olive oil and a pinch of salt and pepper. Place Brussels sprouts and 1 lemon half on a baking sheet. (Reserve remaining lemon for another use.) Roast on top rack until golden brown, 20-25 minutes.
4. Pat steak dry with paper towels; 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. Turn off heat; remove steak from pan and let rest. Wipe out pan.
5. Melt 2 tablespoons butter in the same pan over medium heat. Add remaining garlic and 1 sprig rosemary (2 for 4 servings); cook, stirring, until fragrant, about 1 minute. Reduce heat to low. Add demi-glace, mustard and ¼ cup water (⅓ cup for 4 servings). Cook until thickened, 1-2 minutes. Stir in any resting juices from the steak. Turn off heat; season with salt and pepper. Remove and discard garlic and rosemary.
6. Slice rested steak against the grain. Squeeze juice from roasted lemon half over Brussels sprouts. Sprinkle with lemon zest and chili flakes to taste. Divide steak, Brussels sprouts and mashed potatoes between plates. Spoon sauce over steak and serve.

Recipe Tips

FAQ

Can I use a different cut of steak?

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

What can I use instead of demi-glace?

You can substitute with beef broth thickened with a little cornstarch, but the flavor won’t be as rich.

Can I make this recipe dairy-free?

Yes, use dairy-free butter and sour cream alternatives. The sauce can be made with oil instead of butter.