Steak Sandwich with Caramelized Onions and Horseradish Sauce

Name: Steak Sandwich with Caramelized Onions and Horseradish Sauce
Prep time: 20 min
Cook time: 40 min
Total time: 1 h
Cuisine: American
Ingredients: 1½ pounds flank steak; 1½ teaspoons kosher salt; ¾ teaspoon black pepper; 1 teaspoon garlic powder; 1 tablespoon neutral oil; 2 large yellow onions, thinly sliced; 2 tablespoons unsalted butter; 1 teaspoon brown sugar; 1 tablespoon balsamic vinegar; 4 ciabatta rolls, split; 8 slices provolone cheese; 2 cups baby arugula; ½ cup mayonnaise; ¼ cup sour cream; 2 tablespoons prepared horseradish, drained; 1 teaspoon Dijon mustard; 1 teaspoon fresh lemon juice; ¼ teaspoon kosher salt; ¼ teaspoon black pepper

Published by Fork Around & Find Out Kitchen — presented in the Lila editorial voice. Editorial standards

Quick Answer

Steak Sandwich piles thinly sliced seared flank steak and slow-caramelized onions onto toasted ciabatta with melted provolone and a tangy horseradish sauce.

Jump to Recipe

A steak sandwich only works if the steak understands it is now a sandwich ingredient. That means thin slices, cut across the grain, not a half-inch slab that drags itself out of the ciabatta on the first bite. This version uses flank steak seared hard, rested for ten minutes, and sliced thin before meeting deeply caramelized onions, provolone, arugula, and a horseradish sauce sharp enough to keep all that richness awake.

The onions take the longest and deserve it. Butter, a little brown sugar, and 25–30 minutes over medium-low heat turn two yellow onions deep golden before balsamic vinegar goes in for the final minute. While they cook, the sauce comes together from mayo, sour cream, prepared horseradish, Dijon, lemon, salt, and pepper.

Toast the ciabatta, pile on steak and onions, melt the provolone under the broiler, then add arugula and sauce. The contrast is the point: hot beef, sweet onions, melted cheese, cool peppery greens, and cold tangy horseradish cream. This is not a sandwich for eating while driving unless you have unusually low regard for upholstery.

Prep20 minutes

Cook40 minutes

Total1 hour

Serves4 servings

DifficultyMedium

Ingredients

Servings

1½ pounds flank steak
1½ teaspoons kosher salt
¾ teaspoon black pepper
1 teaspoon garlic powder
1 tablespoon neutral oil
2 large yellow onions, thinly sliced
2 tablespoons unsalted butter
1 teaspoon brown sugar
1 tablespoon balsamic vinegar
4 ciabatta rolls, split
8 slices provolone cheese
2 cups baby arugula
½ cup mayonnaise
¼ cup sour cream
2 tablespoons prepared horseradish, drained
1 teaspoon Dijon mustard
1 teaspoon fresh lemon juice
¼ teaspoon kosher salt
¼ teaspoon black pepper

Instructions

1Stir together the mayonnaise, sour cream, horseradish, Dijon, lemon juice, salt, and pepper. Refrigerate while the sandwich components are prepared.
2Melt the butter in a skillet over medium-low heat. Add the onions and brown sugar. Cook for 25–30 minutes, stirring every few minutes, until deep golden.
3Stir the balsamic vinegar into the onions and cook for 1 minute. Transfer to a bowl.
4Pat the flank steak dry and season with salt, pepper, and garlic powder.
5Heat the oil in a cast-iron skillet over high heat. Cook the steak for 4–6 minutes per side, until 128–133°F for medium-rare. Rest for 10 minutes.
6Toast the ciabatta rolls cut-side down in the skillet for 1–2 minutes.
7Slice the steak very thinly across the grain. Divide it among the bottom rolls and top with caramelized onions and provolone.
8Broil the open sandwiches for 1–2 minutes, until the cheese melts. Add arugula, spread the top rolls with horseradish sauce, and close the sandwiches.

Nutrition Information

Estimated per serving: 1 of 4 servings.

1130Calories

66 gProtein

41 gCarbohydrates

80 gTotal Fat

30 gSaturated Fat

3 gFiber

10 gTotal Sugars

2150 mgSodium

210 mgCholesterol

Estimated from the ingredients and quantities in this recipe using standard food-composition values. Brand choices, trimming, cooking loss, optional ingredients, and actual portion size can change the numbers. How we calculate nutrition estimates.

Pro Tips

Give the onions their full 25–30 minutes over medium-low heat. Rushing with higher heat browns them unevenly instead of building that deep, sweet caramelization.
Slice the rested flank steak thin and against the grain — it's a long-fibered cut, and this is what keeps every bite tender.
Add the arugula and horseradish sauce after broiling, not before. Both are meant to stay cool and fresh against the hot, melty filling.

Substitutions

flank steak → skirt or sirloin steak Both slice well thin; adjust cook time slightly for thickness.

prepared horseradish → horseradish sauce or extra Dijon mustard Prepared horseradish sauce is milder; Dijon swaps the heat for tang.

provolone → Swiss or white cheddar Both melt well and pair nicely with the horseradish sauce.

Storage Instructions

Store the components separately in the refrigerator for up to 3 days — steak, onions, and sauce each in their own container. Reheat the steak and onions before assembling fresh sandwiches.