Preheat your oven to 425°F. Wash the potato, cut it into 1-inch cubes, toss with olive oil, salt, and pepper, and spread evenly on a baking sheet.
Roast the potatoes in the oven for 20-25 minutes or until they are crispy and golden, flipping halfway through.
While the potatoes are roasting, season the 6 oz sirloin steak generously with salt and pepper on both sides.
Heat a heavy skillet over medium-high heat. Once hot, add the steak and sear for about 3-4 minutes per side for medium-rare, or adjust cooking time to your desired doneness.
During the last minute of cooking, reduce the heat to medium-low, add the unsalted butter and minced garlic to the skillet. Spoon the garlic butter over the steak to infuse it with flavor.
Remove the steak from the skillet and let it rest for a few minutes. Slice against the grain if desired.
Plate the steak alongside the crispy roasted potatoes and garnish with freshly chopped parsley. Serve immediately.