Preheat your oven to 425°F.
Wash and dice the white potato into small cubes. Toss the cubes with olive oil, salt, and pepper. Spread them evenly on a baking sheet.
Roast the potatoes in the preheated oven for 20-25 minutes until they are golden and crispy, stirring halfway through.
While the potatoes roast, season the top sirloin steak with salt and pepper on both sides.
Heat a skillet over medium-high heat. Once hot, add the steak and sear for about 3-4 minutes per side or until desired doneness is reached.
In the last minute of cooking, add the unsalted butter and minced garlic (from 2 cloves) to the skillet. Spoon the melting garlic butter over the steak continuously.
Remove the steak from the pan and let it rest for a few minutes.
Plate the steak with a serving of crispy roasted potatoes, drizzle remaining garlic butter from the pan over the steak, and garnish with fresh parsley.
Serve immediately and enjoy your savory meal.