Note: Thaw puff pastry until soft enough to unfold but still cold. Use 1 or 2 sheets, depending on how thick you want the crust.
In a large pot or deep pan, sauté onion in butter until softened. Add garlic and carrot; cook until slightly softened. Sprinkle in flour and mix well.
Add the stock and stir until smooth. Simmer until slightly thickened, then add the chicken.
Add cream and peas. Simmer until the sauce thickens slightly. Season with salt and pepper. Stir in parsley, herbs, or Worcestershire sauce, if using.
Roll out puff pastry on a lightly floured surface. Cut rounds slightly larger than the ramekins.
Divide filling among ramekins or a shallow 2-quart baking dish. Let cool slightly, then brush the edges with egg wash.
Top with puff pastry and press the edges to seal. Cut small slits on top and brush with egg wash.
Bake at 400°F for 20 minutes. Lower the heat to 350°F and bake for another 10 to 20 minutes, or until golden brown.
Cool for about 10 minutes before serving.