Grilled Fingerling Potatoes with Creamy Tarragon Vinaigrette

INGREDIENTS

• 2 tablespoons chopped fresh tarragon leaves, plus leaves for garnish
• 12 fingerling potatoes, par-boiled and halved
• Water, as needed
• 1 tablespoon mayonnaise
• 1 tablespoon chopped shallot
• Salt and freshly cracked black pepper
• 1/4 cup white wine vinegar
• 1/2 cup canola oil, plus more as needed
• 1 tablespoon mustard