Preheat your oven to 425°F (220°C) for the roasted potatoes.
Wash and dice the potato into bite-sized pieces. Toss them with olive oil, salt, and pepper, then spread evenly on a baking sheet.
Roast the potatoes in the preheated oven for about 20-25 minutes, until they are crispy on the outside and tender inside, stirring halfway through.
While the potatoes roast, pat the sirloin steak dry with paper towels. Season both sides with salt and pepper.
Heat a skillet over medium-high heat. Add the unsalted butter and a crushed garlic clove to infuse the butter.
Once the butter is melted and begins to foam, add the steak to the skillet. Sear the steak for about 3-4 minutes on each side or until it reaches your desired doneness.
Remove the steak from the pan and let it rest for a few minutes. Discard the garlic clove from the pan.
Slice the steak against the grain, then plate alongside the roasted potatoes.
Garnish with freshly chopped parsley before serving.