Bistek Tagalog Sandwich

In a bowl, combine the thinly sliced beef sirloin, soy sauce, calamansi juice (or lemon juice), and black pepper. Marinate for at least 15 minutes at room temperature, or up to 30 minutes in the refrigerator.

Heat 1 tablespoon of vegetable oil in a large skillet over medium-high heat. Once hot, sear the marinated beef in batches for 1-2 minutes per side until browned. Do not overcrowd the pan. Remove the seared beef and set aside.

Add the remaining 1 tablespoon of vegetable oil to the same skillet. Reduce heat to medium and add the sliced yellow onions. Cook for 8-10 minutes, stirring occasionally, until the onions are softened and caramelized.

Return the seared beef to the skillet with the caramelized onions. Pour in the remaining marinade and bring to a simmer. Cook for 2-3 minutes, allowing the sauce to slightly reduce and coat the beef and onions.

Lightly toast the bread rolls. Divide the bistek mixture evenly among the toasted rolls and serve immediately.