For the oil: Combine the oil, rosemary, garlic and some salt and pepper in a blender and blend for 2 minutes. Let the oil sit for 30 minutes, and then strain through a fine mesh strainer into a small bowl. Set aside 1/4 cup, plus more as needed, for the home fries, and reserve the rest in an airtight container for another use.
For the home fries: Heat 1/4 cup of the rosemary oil in a large cast-iron skillet over medium heat. Add the pancetta and cook until golden brown and crisp. Transfer to a plate.
Add more rosemary oil to the skillet, if needed. Add the potatoes in one layer and sprinkle with salt and pepper. Cook the potatoes, pressing the firmly with a spatula, until they are golden brown and crusty on the bottom. Turn the potatoes over, and repeat, adding more rosemary oil if needed. Stir in the parsley, red pepper flakes, reserved pancetta and cheese and serve from the pan.