Heat oven to 375°F. Lightly spray 8 (8-oz) individual baking dishes (ramekins) with cooking spray. Place ramekins on cookie sheet.
In 3-quart saucepan, melt butter over medium heat. Add leeks and cook 3 minutes or until tender. Sprinkle with flour; cook, stirring constantly, 3 minutes. Stir in chicken broth. Heat to boiling. Stir in chicken, potatoes, carrots, parsley, salt and pepper. Remove from heat.
On lightly floured surface, cut 8 (4-inch) circles from puff pastry. 4 Divide chicken mixture evenly among ramekins. Top each ramekin with puff pastry and crimp edges. Brush with beaten egg.
Bake on lower oven rack 55 to 60 minutes or until browned. Let stand 15 minutes before serving.