3 Tablespoons of Extra Virgin Olive Oil & 1 Tablespoon of White Wine Vinegar.A good pinch of Salt and Pepper and 1/4 clove of Garlic.You can mix this is in a bowl by hand or put all the ingredients into a blender. 
Serving When the potato salad is finished, taste again for salt & pepper, it may need some more. 

Recipe 2 by Darina Allen Ballymaloe Cookery School
Put all the ingredients into a blender and run at medium speed for 1 minutes approx. or mix oil and vinegar in a bowl, add mustard, salt, freshly ground pepper and mashed garlic. Chop the parsley, spring onion and watercress finely and add in. Whisk before serving.Serving drizzle over a green salad