Preheat your oven to 425°F. Rinse the baby potatoes and cut them in half if they are larger to ensure even roasting.
Toss the potatoes in a small bowl with olive oil, a pinch of salt, and black pepper. Spread them evenly on a baking sheet.
Roast the potatoes in the preheated oven for about 20-25 minutes or until they are golden and crispy, turning once halfway through.
While the potatoes are roasting, pat your 5 oz sirloin steak dry with paper towels and season both sides with salt and black pepper.
Heat a heavy skillet or cast iron pan over medium-high heat. Once hot, add the steak and sear for about 3-4 minutes on each side for medium-rare, adjusting time based on your preferred doneness.
In the final minute of cooking, add the unsalted butter and minced garlic to the pan. Spoon the melted garlic butter over the steak to enhance the flavor.
Remove the steak from the pan and let it rest for a few minutes before slicing.
Plate the steak alongside the crispy roasted potatoes, drizzle any remaining garlic butter from the pan over the steak, and serve immediately.