Preheat your oven to 425°F.
Wash the baby potatoes and cut them in half if they are larger. Place them in a bowl.
Drizzle the potatoes with olive oil, add a pinch of salt, pepper, and half of the minced garlic. Toss to combine.
Spread the potatoes on a baking sheet and roast in the oven for 20-25 minutes until golden and tender.
While the potatoes are roasting, pat the steak dry with paper towels and season generously with salt and pepper on both sides.
Heat a heavy skillet over medium-high heat. Once hot, sear the steak for about 3-4 minutes per side, depending on thickness, until it develops a good crust.
In the last minute of cooking, add the remaining minced garlic, the sprig of rosemary, and the unsalted butter to the skillet. Spoon the melted garlic butter over the steak continuously.
Remove the steak from the skillet and let it rest for a few minutes.
Plate the steak alongside the roasted potatoes, drizzle any remaining garlic butter from the pan over both, and serve immediately.