In a large pot, add the potatoes and cover with enough salted water. Bring to a boil over medium heat and cook for about 15 minutes, this will depend on the size of your potatoes. Once the potatoes are fork tender, drain and set aside to cool slightly.
While the potatoes are cooling, prepare the onion, garlic and fresh parsley. Set aside.
Once the potatoes are cool enough and don't feel that warm to the touch, mix with the mayonnaise and mustard. Stir in the onion, garlic and parsley; and season to taste. Serve the potato salad at room temperature.