Roasted Beef Tenderloin with French Onions and Horseradish Sauce

Picture this: a perfectly roasted beef tenderloin, juicy and tender, paired with sweet, caramelized French onions that melt in your mouth, and a zesty horseradish sauce that adds just the right kick. I still remember the first time I tried this combo—it was like a symphony of flavors dancing on my palate, comforting yet exciting all at once. The magic here is in the contrast: the rich beef, the deep sweetness of slow-cooked onions, and the bright, bold punch of horseradish. Whether it’s a special occasion or you just want to feel fancy at home, this recipe never fails to impress. Trust me, once you master it, it’ll be your go-to for a show-stopping dinner party or a cozy weeknight treat.

Quick Facts

Yield: Serves 6
Prep Time: 20 minutes
Cook Time: 35 minutes
Total Time: 55 minutes

Ingredients

For the Main Dish:

3-pound beef tenderloin, trimmed
2 tbsp olive oil
Salt and freshly ground black pepper, to taste
2 sprigs fresh rosemary
2 cloves garlic, smashed

For the French Onions:

3 large yellow onions, thinly sliced
2 tbsp unsalted butter
1 tbsp olive oil
1 tsp sugar
Salt, to taste
¼ cup dry white wine or beef broth

For the Horseradish Sauce:

½ cup sour cream
2 tbsp prepared horseradish (adjust to taste)
1 tsp Dijon mustard
1 tbsp lemon juice
Salt and pepper, to taste

How I Make It

Step 1:

Start by preheating your oven to 425°F. Pat the beef tenderloin dry with paper towels—this helps the crust develop beautifully. Rub it all over with olive oil, salt, and pepper. Nestle the rosemary and garlic around the meat for added aroma.

Step 2:

While the oven heats, heat a large skillet over medium-high heat. Sear the tenderloin on all sides until it gets a deep golden crust, about 3 minutes per side. This step locks in those flavorful juices.

Step 3:

Transfer the beef to a roasting pan and pop it into the oven. Roast until the internal temperature reaches 125°F for medium-rare (about 20-25 minutes). Don’t skip the thermometer here—oven times vary!

Step 4:

While the beef roasts, let’s tackle the onions. Melt the butter and olive oil in a large pan over medium heat. Add the sliced onions and sprinkle the sugar and salt over them—this helps caramelize and bring out their natural sweetness. Stir occasionally, cooking until they’re soft and golden brown, about 25 minutes.

Step 5:

Add the white wine or beef broth to deglaze the pan, scraping up any browned bits—it adds an amazing depth of flavor. Cook until the liquid evaporates, then remove from heat.

Step 6:

By now, the tenderloin should be resting—tent it with foil and let it sit for 10-15 minutes to redistribute those juices. Mix up your horseradish sauce by whisking together sour cream, horseradish, Dijon, lemon juice, salt, and pepper. Slice the beef, arrange it on a platter, top with the luscious French onions, and serve with a dollop of horseradish sauce on the side.

Variations & Tips

Swap fresh rosemary with thyme or sage for a different herbal note.
Use shallots instead of onions for a milder, sweeter flavor in the French onions.
Add a splash of brandy or sherry when deglazing the onions for extra richness.
For a creamier sauce, stir in a tablespoon of mayonnaise or Greek yogurt.
If you like more heat, mix a dash of hot sauce or black pepper into the horseradish sauce.
Rest the tenderloin longer if you prefer your beef medium instead of medium-rare.

How I Like to Serve It

This dish is fantastic with classic mashed potatoes or buttery roasted vegetables to soak up all those delicious juices. I love serving it when friends come over—it’s elegant but still feels like a warm hug on a plate. It’s equally perfect for a holiday feast or a special weekend dinner when you want to celebrate something special without too much fuss.

Notes

Store leftovers wrapped tightly in the fridge for up to 3 days; reheat gently to avoid drying out.
If you can’t find beef tenderloin, filet mignon steaks make a great smaller portion substitute.

Closing: This roasted beef tenderloin with French onions and horseradish sauce is one of those recipes that feels fancy but is surprisingly simple, and it always delivers that wow-worthy flavor every time I serve it.