Chicken Pot Pie Soup

Name: Chicken Pot Pie Soup
Ingredients: 3 chicken breasts, skin-on, bone-in (2 1/2 to 3 pounds total); Good olive oil; Kosher salt and freshly ground black pepper; 6 tablespoons (3/4 stick) unsalted butter; 5 cups chopped leeks, white and light green parts (3 leeks) (see Cook’s Note); 4 cups chopped fennel, tops and cores removed (2 bulbs); 3 cups (1/2-inch) diced scrubbed carrots (5 medium); 1 tablespoon minced garlic (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-by-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; Puff Pastry Croutons (recipe follows); 1 sheet of frozen puff pastry, such as Pepperidge Farm, defrosted; 1 extra-large egg beaten with 1 tablespoon heavy cream, for egg wash