• Preheat the oven to 425°F.

Prepare the Filling

• Heat an oven-proof skillet over medium heat and melt the butter.
• Add in the onion, carrot, celery, and potatoes. Cook for about 5 minutes, stirring often for even cooking.
• Add ¼ cup of water and cover the skillet to allow the vegetables to steam for about 3 minutes on medium-low.
• Remove the cover and add the flour, salt, pepper, thyme, and sage. Cook, stirring frequently, for one minute.
• Add in the half and half in a slow stream, stirring constantly and scraping the bottom of the skillet to get a smooth sauce.
• Stir in the chicken and peas and taste the filling. Adjust seasoning if desired and remove the filling from the heat.

Puff Pastry Crust

• Unroll the puff pastry sheet. If desired, cut the sheet into diamonds and arrange them into a circle big enough to cover your skillet.
• Invert the arranged puff pastry over the skillet and make sure the filling is covered.
• Alternatively, unroll the sheet of pastry and drape it over the skillet and filling, trimming the edges if needed.
• Whisk the egg in a small bowl with one tablespoon of water and brush the surface of the pot pie with the egg wash.

Baking the Pot Pie

• Transfer the skillet to a sheet pan and bake for 30-35 minutes, until the puff pastry is golden brown.
• Allow the pot pie to rest for five minutes before serving.