Place cubed potatoes on a large baking sheet and drizzle with 2 of the 3 Tbsp of olive oil. Toss to coat well and season with salt and pepper. Be sure potatoes are spread out in an even layer.
Place in the oven and bake for 25 minutes.
Remove from oven and drizzle with remaining 1 Tbsp of oil. Sprinkle with parmesan, garlic, and rosemary. Toss until well coated and spread into a single layer.
Return to the oven and bake for 15 more minutes until tender and lightly brown. Serves 4-5