To make the 'aioli' sauce (food processor recommended) with a processor, fining mince the garlic and add to the egg yoke, vinegar, pepper (and maybe a pinch of salt) to a bowl -- mix very well. Slowly add in oil a few tbsp's at a time, mixing well.
To prepare the potatoes, slice in half or quarters depending on their size (should be bite sized), place in a large pot of cold water, salted, and bring to a boil. Lower heat and let simmer of around 8 minutes or until tender. Drain well, and pour into sauce, tossing the potatoes in the sauce to ensure an even mixture. Let stand for 15 or 20 minutes, sprinkle over the fresh parsley and serve.