Chicken Pot Pie Soup with Puff Pastry Croutons

Ingredient:

• All-purpose flour, for dusting
• 1 sheet of frozen puff pastry, such as Pepperidge Farm, defrosted (see note)
• 1 extra-large egg beaten with 1 tablespoon heavy cream, for egg wash
• Kosher salt
• Freshly ground black pepper
• 3 chicken breasts, skin-on, bone-in (2 1/2 to 3 pounds total)
• Good olive oil
• 6 tablespoons (3/4 stick) unsalted butter
• 5 cups chopped leeks (about 3 leeks), white and light green parts (see note)
• 4 cups chopped fennel (about 2 bulbs), tops and cores removed
• 3 cups (1/2-inch) carrots, scrubbed and diced
• 1 tablespoon minced garlic (about 3 cloves)
• 1 tablespoon chopped fresh tarragon leaves
• 1/4 cup Wondra flour
• 3/4 cup cream sherry, divided
• 7 cups good chicken stock, preferably homemade
• 1 (2- × 3-inch) piece of Italian Parmesan cheese rind
• 1 (10-ounce) box frozen peas
• 1 cup frozen whole pearl onions
• 1/4 cup minced fresh parsley