A Simple Chicken Pie

I created this pie for dinner last night. Mr. Fox and I thought it was too good not to share! The ingredients I used are listed below -- feel free to experiment! Ingredients for about 6 servings: For the chicken: Approximately 2 1/2 lbs cooked, shredded chicken -- I used a combination of chicken thighs and breasts. For the vegetables: A 16-ounce bag of mixed, frozen peas and carrots 2-3 cups diced potatoes (mine came frozen in a bag) For the thick white sauce: 3 cups whole milk 1/2 teaspoon salt and grinds of black pepper 1 teaspoon onion powder 1/2 to 1 teaspoon dried tarragon leaves 4 generous tablespoons cornstarch blended with just enough water to make a smooth slurry For the crust: A sheet of frozen puff pastry dough, thawed but still quite cold (I used gluten-free puff pastry because Mr. Fox requested it)