American potato salad

Ingredients

• 1 kg new or red potatoes
• 80 ml olive oil
• 5 cornichons or small pickles
• 2 shallots
• 5 radishes
• 20 g tarragon
• 20 g flat-leaf parsley
• 20 g chives, plus more for garnish
• 2 tbsp grainy mustard
• 2 tsp Dijon mustard
• 3 tbsp apple cider vinegar
• ½ tsp sugar