In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the diced russet potatoes and sauté until golden brown and tender, about 10-12 minutes. Stir occasionally to ensure even cooking. Once done, remove the potatoes from the skillet and set them aside.
In the same skillet, add the remaining tablespoon of olive oil. Increase the heat to medium-high and add the thinly sliced beef sirloin or flank steak. Season with salt and pepper. Cook until browned on both sides, about 4-5 minutes. Remove the beef from the skillet and set it aside with the potatoes.
In the same skillet, add the sliced onion and sauté until translucent, about 3 minutes. Add the minced garlic and sauté for an additional minute until fragrant.
Stir in the sliced jalapeños, chopped Roma tomatoes, ground cumin, and dried oregano. Cook for another 3-4 minutes until the tomatoes are softened.
Return the cooked beef and potatoes to the skillet. Pour in the tomato sauce and stir to combine. Reduce the heat to low and let everything simmer for about 10 minutes, allowing the flavors to meld together.
Once the Bistec Ranchero is ready, remove it from heat and garnish with freshly chopped cilantro. Serve hot with warm tortillas, rice, or your favorite side dishes.
