Flank Steak Sandwich Recipe

Prep marinade

In a shallow dish or zip-top bag combine 3 tbs olive oil, 2 tbs soy sauce, 1 tbs balsamic vinegar, 1 tbs Worcestershire sauce, 3 crushed garlic cloves, 1 tsp chopped fresh rosemary, 1 tsp black pepper and 1 tsp salt. Whisk or shake to emulsify.

Marinate steak

Place 1 lb flank steak in the marinade, turning to coat thoroughly. Refrigerate and marinate for at least 30 minutes and up to 4 hours. Remove from fridge 20 minutes before cooking to come toward room temperature.

Cook steak

Preheat a cast-iron skillet or grill over medium-high heat until very hot. Pat steak dry with paper towels to ensure good sear. Add a light coat of oil to the pan or brush on the steak. Sear flank steak 4-5 minutes per side for medium-rare (internal temp 130-135°F / 54-57°C) depending on thickness. Adjust time for desired doneness.

Rest & slice

Transfer steak to a cutting board and tent loosely with foil. Let rest 8-10 minutes. Slice thinly across the grain into 1/8–1/4 inch slices.

Caramelize onions & mushrooms

While the steak rests, heat 2 tbs unsalted butter in a skillet over medium heat. Add 1 medium thinly sliced yellow onion and a pinch of salt; cook, stirring occasionally, until soft and beginning to brown, about 8-10 minutes. Add 4 oz sliced baby bella mushrooms and 1 minced garlic clove; cook until mushrooms release liquid and it reduces, another 5-6 minutes. Stir in 1 tsp fresh thyme.

Deglaze and make jus

Pour in 1 cup beef broth to deglaze the pan, scraping up browned bits. Simmer until reduced by about one-third and slightly thickened, 4-6 minutes. Taste and season with 1/2 tsp salt and 1/4 tsp black pepper. Keep warm.

Make horseradish mayo

In a small bowl combine 2 tbs mayonnaise, 1 tsp prepared horseradish and 1 tsp Dijon mustard. Mix until smooth and refrigerate until assembly.

Prepare rolls

Preheat oven to 375°F (190°C) or heat a skillet. Split 4 ciabatta rolls horizontally. Brush cut sides lightly with 1 tbs olive oil. Toast cut-side down in oven or skillet until golden, 3-5 minutes.

Assemble sandwiches

Spread a thin layer of horseradish mayo on both cut sides of each toasted roll. Pile sliced flank steak evenly among rolls. Spoon warm onion-mushroom jus over the steak (about 2-3 tbs per sandwich). Top each with a slice of provolone cheese and a small handful of arugula.

Finish

If desired, place assembled sandwiches under a broiler or in a hot oven for 1-2 minutes to melt cheese. Serve immediately while steak and jus are warm.