The main difference in this pesto, of course, is its base - purple basil. Compared to green basil, purple basil has a slightly sharper and less minty flavor, giving the sauce a richer depth.
Roast the pine nuts for about 4 minutes until golden in a dry frying pan over medium heat and set aside.
In a mortar, mash the garlic, add the basil and nuts. Mash everything together.
Grate the cheese and add to the mortar. Gradually add the olive oil to the contents of the mortar, mixing until the desired consistency is reached. Season to taste with salt and pepper and mix well.