Preheat your oven to 350 degrees. Melt the butter in a medium sized pot over medium heat. Once the butter has melted, add the onions and cook for 3 minutes before adding the mushrooms. Season with salt and pepper and saute for 8 minutes.

Next, add the cream of mushroom soup and the chicken broth. Stir the soup and broth together, and heat to a simmer. Add the remaining vegetables and the chicken. Let simmer and reduce for about 5 minutes.

Pour the pie filling into your pie pan or ramekins. Top with the puff pastry or pie crust. Cut a few slits in the crust so steam can escape. Brush the crust with the melted butter. Bake for 35-45 minutes until the crust has browned.