3 cups fat-free, less-sodium chicken broth
1 1/2 cups frozen green peas, thawed
1 cup (1/2-inch) cubed peeled baking potato
1 cup (1/2-inch) cubed peeled sweet potato
1 cup (1/2-inch) cubed peeled celeriac (celery root)
1 cup (1/2-inch-thick) slices parsnip
1 (10-ounce) package frozen pearl onions
1 pound skinless, boneless chicken breasts, cut into bite-sized pieces
2/3 cup all-purpose flour (about 3 ounces), divided
1 1/2 cups fat-free milk
1/4 cup chopped fresh parsley
2 tablespoons chopped fresh thyme
1 1/2 teaspoons salt
1 teaspoon freshly ground black pepper
Cooking spray
1 sheet frozen puff pastry dough, thawed