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Roasted Beef Tenderloin with French Onions and Horseradish Sauce

Alright, I have to confess: there’s something downright magical about roasting a beef tenderloin that just fills the kitchen with a warm, savory aroma you want to bottle up forever. I remember my first time cooking one—it felt fancy, a bit intimidating, but oh so rewarding once that crusty, caramelized exterior met the tender, juicy inside. Paired with sweet, slow-cooked French onions and a sharp, creamy horseradish sauce, this dish feels like a cozy celebration on a plate. Whether you’re treating yourself or a crowd, this recipe brings a comforting elegance without any fuss. Stick with me, and I’ll walk you through every step so your kitchen smells incredible and the flavors truly sing!

Quick Facts

Yield: Serves 6
Prep Time: 20 minutes
Cook Time: 35-45 minutes
Total Time: 1 hour

Ingredients

For the Main Dish:

1 (3 to 4-pound) beef tenderloin, trimmed
2 tbsp olive oil
1 tbsp kosher salt
1 tsp freshly ground black pepper
2 tsp garlic powder
2 sprigs fresh rosemary or thyme (optional)

For the French Onions:

3 large yellow onions, thinly sliced
3 tbsp unsalted butter
1 tbsp olive oil
1 tsp sugar
1/2 cup beef broth or water
Salt and pepper, to taste

For the Horseradish Sauce:

1/2 cup sour cream
2 tbsp prepared horseradish (adjust to taste)
1 tbsp lemon juice
Salt, to taste

How I Make It

Step 1:

First things first: preheat your oven to 425°F. Pat the beef tenderloin dry with paper towels—this helps create that beautiful brown crust. Rub the entire roast with olive oil, kosher salt, black pepper, and garlic powder. If you have rosemary or thyme, tuck the sprigs around the roast for an extra herbaceous hint as it cooks.

Step 2:

Place the tenderloin on a roasting rack inside a baking pan. Roast it in the preheated oven for about 35 to 45 minutes, or until an instant-read thermometer inserted into the thickest part reads 135°F for medium-rare. Remember, the beef will carry over a few degrees while resting!

Step 3:

While the beef is roasting, melt butter and olive oil together in a large skillet over medium heat. Add the sliced onions, stir to coat, then cook slowly until soft and deeply caramelized—this takes about 30 to 40 minutes. Sprinkle in the sugar after the first 10 minutes to help with caramelization. Pour in the beef broth near the end to deglaze the pan and add moisture. Season with salt and pepper to taste.

Step 4:

Once the tenderloin comes out of the oven, tent it loosely with foil and let it rest for at least 15 minutes. This step is key—it lets the juices redistribute, giving you perfectly juicy slices every time.

Step 5:

While the beef rests, whip up the horseradish sauce by stirring together sour cream, prepared horseradish, lemon juice, and salt. Taste and add more horseradish if you want that extra kick.

Step 6:

Slice the rested tenderloin into thick medallions, plate with a generous mound of caramelized French onions, and a dollop of horseradish sauce on the side. Enjoy the fantastic contrast of tender beef, sweet onions, and tangy creaminess!

Variations & Tips

For an even crustier exterior, sear the tenderloin in a hot pan for 2-3 minutes per side before roasting.
Use shallots instead of onions for a slightly sweeter, more delicate flavor in the caramelized onions.
Swap sour cream with Greek yogurt in the horseradish sauce for a tangier, lighter dip.
If you like your beef more well done, remove from the oven at 140°F for medium.
Make the French onions a day ahead—the flavors deepen beautifully after resting.
Leftover beef tenderloin makes amazing steak sandwiches the next day!

How I Like to Serve It

This dish is perfect for a special Sunday dinner or holiday feast when you want to impress without stressing. I love pairing it with roasted garlic mashed potatoes and a crisp green salad to balance out the richness. On chilly evenings, a glass of full-bodied red wine doesn’t hurt, either!