Wash your basil leaves and dry them of excess water by placing them on a paper or kitchen towel. Grate your cheese, crush garlic cloves with a knife to make it easier to mash in the mortar.
Put the basil leaves and garlic into a mortar or a blender and start mashing them.
When you get a mushy consistency with some bits of basil leaves in it, add the pine nuts and continue mashing. Pine nuts will absorb most of the moisture content of the basil leaves, and your mixture is getting to look more and more like a real pesto Genovese.
Add the grated cheese and continue mashing. At the end of this stage your pesto will be quite dry.
At last, add the extra virgin olive oil and stir thoroughly.