An easy cheesy filling

Ideal for summer sandwiches

Materials

• 2 kg Boneless beef steak or Flank steak, very thinly sliced
• 1½ teaspoons of salt
• ½ teaspoon freshly ground pepper
• ½ kilo mushrooms, quartered
• 3 tablespoons of virgin olive oil
• 1 medium yellow onion, thinly sliced
• 1 green pepper, thinly sliced
• 1 red pepper, thinly sliced
• 4 cloves of garlic, chopped or less depending on your preferences
• 2 cups shredded mozzarella
• ½ cup grated parmesan
• 4 spring onions, thinly sliced ​​(optional)
• 6 shortbread rolls, toasted (optional)

Step by step process

1. Season the steak all over with 1 teaspoon salt and pepper.
2. Heat a medium, oven-safe frying pan over medium-high heat and add the mushrooms to the dry pan. Sprinkle with the remaining ½ teaspoon salt and cook until golden brown, about 5 minutes.
3. Increase the heat to high, add 2 tablespoons of olive oil to the pan. When the oil shimmers, add the onions and peppers and cook, stirring occasionally, until the onions and peppers begin to soften, 3-5 minutes. Transfer the vegetables to a plate.
4. In the same pan, add the remaining 1 tablespoon olive oil over high heat. Once the oil is shimmering, add the steak in small batches, cook for 1-2 minutes per side, until browned, transfer to a plate.
5. Repeat with the remaining steak.
6. Reduce the heat to medium, add the garlic, and cook, stirring, until fragrant, about 1 minute more.
7. Return the vegetables and steak, along with any accumulated juices, back to the pan and toss to combine.
8. Cover evenly with mozzarella and parmesan.
9. Light the grill with a rack in the middle position. Place the pan in the oven and bake until the cheese is melted and bubbly. Sprinkle with spring onions, if preferred.
10. Serve the filling warm, divided between the buns, or you can also accompany it with french fries.