Thanksgiving Leftover Pot Pies

Name: Thanksgiving Leftover Pot Pies
Ingredients: 1 sheet frozen puff pastry (half of a 17-ounce package), thawed; All-purpose flour, for dusting; 1 large egg; Kosher salt and black pepper, to taste; 2 tbsp. salted butter; 3 celery stalks, finely chopped; 2 carrots, finely chopped; 1 c. low-sodium chicken broth; 1 c. leftover gravy; 1 c. half-and-half; 4 c. chopped leftover turkey, skin removed; 1 c. chopped leftover green been casserole or other cooked green beans; 1 c. frozen peas; 3 tbsp. chopped fresh parsley; Squeeze of lemon juice