Pappardelle with Chicken and Mushroom Ragu

INGREDIENTS

• 6 ounces cremini mushrooms
• 3 garlic cloves
• 1/4 cup extra-virgin olive oil
• 1 1/4 pounds skinless boneless chicken thighs, cut into 1/2-inch pieces
• 1 small onion, chopped
• 3/4 teaspoon chopped rosemary
• 3 tablespoons balsamic vinegar
• 1 (28-ounce) can whole tomatoes in juice
• 1/2 pound dried pappardelle (or penne is just fine too)
• 5 ounces baby arugula (about 8 cups)
• Accompaniment: Grated Parmigiano-Reggiano