Pan-Seared Steak Sandwich with Caramelized Onions and Horseradish Mayo

By AislePrompt Editorial · Published 2026-04-25 · Updated 2026-04-25

Tender pan-seared flank steak layered with sweet caramelized onions and a spicy horseradish mayo on toasted ciabatta rolls. This American-inspired sandwich and wrap recipe, ready in about 35 minutes, pairs flank steak, salt, black pepper for a weeknight-friendly dinner that comes together with one pan and minimal cleanup. Each serving lands at about 700 calories and feeds 2, so it slots cleanly into a weekly meal plan and pairs well with a quick salad or grain on the side. Tap "Plan a meal with the AI" below to drop this recipe into your week and send the ingredients straight to Instacart. Nutrition values are approximate, calculated from USDA FoodData Central (fdc.nal.usda.gov) — verify against ingredient labels for any health-driven dietary plan.

Ingredients

• 8 oz flank steak
• 1 tsp salt
• 1/2 tsp black pepper
• 2 tbsp olive oil
• 1 large, thinly sliced yellow onion
• 1 tbsp unsalted butter
• 3 tbsp mayonnaise
• 1 tbsp prepared horseradish
• 2 ciabatta rolls
• 1 cup arugula

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Instructions

1. Step 1: Season 8 oz flank steak evenly with 1 tsp salt and 1/2 tsp black pepper on both sides.
2. Step 2: Heat 1 tbsp olive oil in a cast-iron skillet over medium-high heat until shimmering. Add steak and sear for 4-5 minutes per side for medium-rare, or until desired doneness; remove and let rest 5 minutes before slicing thinly against the grain.
3. Step 3: In the same skillet, reduce heat to medium, add 1 tbsp unsalted butter and 1 tbsp olive oil, then add 1 large thinly sliced yellow onion. Cook, stirring occasionally, for 12-15 minutes until onions are golden brown and caramelized.
4. Step 4: In a small bowl, combine 3 tbsp mayonnaise with 1 tbsp prepared horseradish until smooth.
5. Step 5: Slice 2 ciabatta rolls in half and toast cut sides in a dry pan over medium heat for 2 minutes until lightly crisp.
6. Step 6: Spread horseradish mayo generously on bottom halves of rolls. Layer arugula leaves, generous slices of steak, and caramelized onions. Top with remaining roll halves and serve warm for a savory, spicy sandwich.