Quicker Chicken Pot Pie

Why I Love This Recipe
This is an adaptation of a recipe I saw on RACHAEL RAY. I exchanged mushrooms for peas, poultry seasoning for tarragon, and replaced her polenta topping with puff pastry. It came out wonderfully and required minimal effort.
Ingredients You'll Need
1 lb. (approx.) chicken tenders or boneless/skinless breast, cut in bite-size pieces
2 medium carrots, diced
1 medium onion, diced
2 stalks celery, diced
8-10 button mushrooms, sliced
2 Tbl. vegetable oil
1 teasp. poultry seasoning
2 Tbl. butter
2 Tbl. flour
2 cups chicken broth
1/2 cup half & half or cream
1 Tbl. Dijon mustard
1 sheet frozen puff-pastry (like Pepperidge Farm) thawed as per directions on box
Directions
Pre-heat oven to 400F.
In a large skillet, heat the vegetable oil and add chicken pieces, browning lightly on all sides for a few minutes. Add the onion, carrots and celery to the pan and continue to cook until vegetables are softened, about 10 minutes. Now add the mushrooms and poultry seasoning and continue to cook for another minute or two, until mushrooms have cooked and browned a bit. Push the mixture off to one side of the skillet, and in the vacant area, melt the butter. Mix the flour into the butter to create a roux, and allow to cook for a minute. Add the chicken broth, whisking to eliminate any lumps. Add in the cream and bring mixture to a boil. Allow to cook for a minute or two to thicken.
Choose an oven-proof casserole large enough to accommodate the mixture and spoon in the hot chicken/vegetable mixture. While the filling cools slightly, lay out the sheet of thawed pastry on a lightly floured surface. With a lightly floured rolling pin, roll out the dough to fit the top of the casserole dish, extending slightly over the edges. Brush crust with a little milk or cream and make several cuts to vent.
Bake about 20 minutes, until crust is puffed and golden brown