How to make
Wash the potatoes and put them to boil in 5 cups (1.2 L) of cold water. Let them boil at the highest possible temperature, season with salt, then reduce to medium heat. Blanch the 2 cloves of garlic in the water for about a minute, cool them with water and peel.
Boil the potatoes until slightly tender - they need to remain hard instead of soft and overcooked. Drain the potatoes, keeping 1/4 of the water in which you boiled them.
Place the potatoes in a baking tray and crush the garlic and onion. To the potato water, add the garlic, onion, vinegar, mustard, olive oil and black pepper and mix to obtain a homogeneous mixture.
Pour this dressing over the warm potatoes and put them to bake. Shortly before they are ready, sprinkle them with more black pepper, salt, tarragon and parsley, then slightly mix and leave them for about 5 minutes to bake until finished.
