In a large pot, combine the diced potatoes with enough salted water to cover them completely. Bring to a vigorous boil and cook for approximately 10-12 minutes, or until easily pierced with a fork. Drain and set aside.
Season the sirloin steak cubes generously with salt and pepper. Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the steak cubes in batches, searing for 2-3 minutes on each side until a golden brown crust forms. Remove from skillet and set aside.
In the same skillet, lower the heat to medium. Add the unsalted butter, minced garlic, chopped rosemary, and chopped thyme. Stir for about 1-2 minutes until the garlic is aromatic and the butter melts completely.
Return the seared steak to the skillet and add the drained potatoes. Gently toss to coat everything in the garlic butter sauce. Cook for an additional 2-3 minutes, stirring occasionally.
Remove from heat and sprinkle with chopped parsley before serving.
Notes
For an appealing presentation, serve in a rustic cast iron skillet or on a wooden serving board.