2Melt butter in a skillet over medium-low heat, and cook until the onion and garlic are tender, about 15 minutes, stirring occasionally. Stir in the frozen vegetables and the diced potatoes. Stir in the flour and cook, stirring constantly, until the flour coats the vegetables and begins to fry, about 5 minutes. Whisk in chicken broth, thyme, and half-and-half. Cook until the sauce is thick and bubbling. Season to taste with salt and black pepper, and mix in the chicken meat.
3Line a 2-quart casserole dish, that has been sprayed with Pam, with one of the pie crusts. Pour the chicken/vegetable mixture into the crust and top with the second crust. Seal the crusts together and cut slits in the top crust to vent for steam. Brush the top crust with milk.
4Bake in the oven for approximately 1 hour and the pie filling is bubbling and the crust is brown.. Let rest 10 minutes before serving.
I sometimes will omit the frozen vegetables and substitute one 16-ounce can of peas and carrots, drained and 1 8-oz. can mushroom bits and pieces, drained.