Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Dice the yellow potato into 1/2-inch cubes. Toss them on the baking sheet with 1 teaspoon of olive oil and half of the sea salt and black pepper.
Roast the potatoes for 20-25 minutes, flipping halfway through, until they are golden brown and crispy.
While potatoes roast, trim the woody ends off the asparagus and mince the garlic cloves.
Pat the sirloin steak dry with a paper towel and season both sides with the remaining sea salt and black pepper.
Heat the remaining 1 teaspoon of olive oil in a cast-iron skillet over medium-high heat. Once the pan is shimmering, add the steak.
Sear the steak for 3-4 minutes per side for medium-rare. During the last 2 minutes of cooking, add the minced garlic and fresh rosemary sprig to the pan, spooning the infused oil over the steak.
Remove the steak from the pan and let it rest on a cutting board for at least 5 minutes.
In the same skillet used for the steak, quickly sauté the asparagus for 3-4 minutes until tender-crisp, picking up the remaining garlic flavors.
Slice the steak against the grain and serve alongside the roasted potatoes and sautéed asparagus.