Steak with Mushroom Sauce and Caramelized Onion Mashed Potatoes

This steak dinner is all about rich, savory flavors and comforting sides. A perfectly seared sirloin steak is topped with a luscious mushroom pan sauce that’s both earthy and tangy from a touch of Dijon mustard. On the side, creamy mashed potatoes get a sweet and savory upgrade with caramelized onions, while roasted carrots add a tender, slightly sweet contrast.

Every element comes together for a satisfying meal that feels special enough for a weekend dinner but is simple enough for a weeknight. The key is building layers of flavor-from the caramelized onions to the pan sauce that picks up all the delicious browned bits from the steak.

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Ingredients

1 unit Yellow OnionView ingredient guideLike ingredientDislike ingredient

2 clove GarlicView ingredient guideLike ingredientDislike ingredient

12 ounce CarrotsView ingredient guideLike ingredientDislike ingredient

4 ounce Button MushroomsView ingredient guideLike ingredientDislike ingredient

16 ounce Yukon Gold PotatoesView ingredient guideLike ingredientDislike ingredient

6 tablespoon Sour CreamView ingredient guideLike ingredientDislike ingredient

14 ounce Sirloin SteakView ingredient guideLike ingredientDislike ingredient

1 unit Beef Demi-GlaceView ingredient guideLike ingredientDislike ingredient

2 teaspoon Dijon MustardView ingredient guideLike ingredientDislike ingredient

2 tablespoon Vegetable OilView ingredient guideLike ingredientDislike ingredient

3 tablespoon ButterView ingredient guideLike ingredientDislike ingredient

SaltView ingredient guideLike ingredientDislike ingredient

PepperView ingredient guideLike ingredientDislike ingredient

1 teaspoon SugarView ingredient guideLike ingredientDislike ingredient

Instructions

1. Adjust an oven rack to the top position and preheat to 425°F. Wash and dry all produce. Halve, peel and thinly slice the onion. Mince the garlic. Peel and cut the carrots on a diagonal into 1-inch-thick pieces. Trim and thinly slice the mushrooms. Peel and dice the potatoes into ½-inch pieces. (Tip: For speedier prep, you can skip peeling the potatoes.)
2. Toss the carrots on a baking sheet with a large drizzle of oil, salt and pepper. Roast on the top rack, flipping halfway through, until tender, 25-30 minutes. Meanwhile, place the potatoes in a medium pot and add enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes. Drain well and return the potatoes to the pot.
3. While the potatoes cook, heat a large drizzle of oil in a medium nonstick pan over medium-high heat. Add the onion and cook, stirring occasionally, until browned and softened, 8-10 minutes. Add 1 teaspoon sugar (2 teaspoons for 4 servings) and a splash of water; cook until caramelized, 2-3 minutes more. Season with salt and pepper. Transfer to a small bowl and wipe out the pan.
4. Place the pot with the potatoes over low heat. Mash with the sour cream, salt and pepper until smooth. Keep covered until ready to serve. Pat the steak dry with paper towels and season all over with salt and pepper. Heat a large drizzle of oil in the same pan used for the onion over medium-high heat. Add the steak and cook until browned, 3-6 minutes per side. Transfer the steak to a second baking sheet. Roast until cooked to your desired doneness, 4-7 minutes. Let rest.
5. Melt 2 tablespoons butter (3 tablespoons for 4 servings) in the pan used for the steak over medium-high heat. Add the mushrooms and cook, stirring, until softened, 2-4 minutes. Add the garlic and cook until fragrant, 30 seconds to 1 minute. Stir in the demi-glace and ¼ cup water (⅓ cup for 4 servings). Bring to a boil, then reduce to a low simmer. Stir in the mustard. Simmer until slightly thickened, 3-4 minutes. Turn off the heat and stir in 1 tablespoon butter until melted.
6. Slice the steak against the grain. Divide the potatoes, carrots and steak between plates. Top the potatoes with the caramelized onion. Spoon the mushroom sauce over the steak, making sure to include the mushrooms and serve.

Recipe Tips

FAQ

Can I use a different cut of steak?

Yes, you can substitute sirloin with ribeye, strip steak or filet mignon. Adjust cooking time based on thickness.

What can I use instead of demi-glace?

You can substitute with 1 cup beef broth simmered until reduced by half or use 1 tablespoon soy sauce mixed with 1 cup beef broth for a similar savory depth.

Can I make this recipe dairy-free?

Yes, use dairy-free sour cream and butter alternatives. The sauce will still be delicious with olive oil instead of butter.