450g frozen puff pastry, thawed according to package directions
1 egg
1 tablespoon milk or water
Directions
Place a large skillet over medium heat. Melt in the butter and add the leek or onion, celery, and carrot, season with salt and pepper, and cook for 5 to 6 minutes or until softened and lightly golden. Stir in the garlic and cook for another minute.
Stir in the flour and allow it to toast for 1 minute. Switch to a whisk and slowly whisk in the chicken broth. Add the chicken to the pan along with the peas, parsley, Parmigiano-Reggiano, and sour cream. Season with salt and pepper, bring to a simmer, and cook until thickened. You want the stew to be quite thick. Set aside to cool completely. If desired, you can make the stew up to two days in advance and store in the fridge.
Arrange your oven rack to the lowest position and heat the oven to 425ºF. Line a sheet pan with parchment paper and set aside.
If your puff pastry comes in 2 sheets or blocks, roll each out into a 9-by-14-inch rectangle and cut each into six roughly 4 1/2-inch squares. If your pastry comes as 1 large sheet, roll into a 14-by-18-inch rectangle and cut into 12. Divide the chicken stew evenly into the center of each square and fold over into a triangle, pressing the edges with a fork to seal. Transfer to the prepared sheet pan.
Beat the egg with the milk or water and brush the tops of each hand pie with a thin layer of egg wash. Cut a small slit in the top of each to allow steam to escape and bake the hand pies on the bottom rack for 20 minutes or until golden and crisp.
Allow to cool slightly or all the way to room temperature before serving.
