Sunchoke and Potato Salad

Ingredients

• 3 tablespoons coarsely chopped hazelnuts
• 2 tablespoons minced shallot
• 1/4 teaspoon grated garlic
• 2 tablespoons red wine vinegar
• Salt
• 14 ounces (395 g) 2-inch (5-cm) sunchokes, scrubbed and trimmed
• 14 ounces (395 g) small butterball potatoes
• 4 tablespoons olive oil, plus more for the baking sheet
• 1 teaspoon minced fresh rosemary
• 2 cups (70 g) watercress, thick stems removed
• Cracked black pepper