Preheat the oven to 400°F. Melt 2 tablespoons of the butter in a large heavy skillet.

Add leeks, carrots and celery and cook over medium heat until softened but not browned, about 10 minutes.

Transfer vegetables to a bowl and set aside. Melt remaining 1 tablespoon butter in skillet.

Add mushrooms and cook over medium high heat until they have given off their moisture and are tender, about 10 minutes.

Add leek mixture to skillet and toss to combine.

Add flour, stir well and cook for 1 minute.

Slowly add broth while stirring constantly. Bring to a simmer and cook, stirring constantly, until thickened, about 5 minutes.

Add turkey, all but 1 tablespoon of the cream, thyme, salt and pepper and stir well.

Transfer contents of skillet to a large bowl and set aside to let cool.

Remove pie crusts from the freezer and set one aside to let thaw.

Fill remaining pie crust with cooled turkey mixture and moisten the edges with a bit of water.

When remaining pie crust is thawed but still cold, invert pie pan on top of turkey mixture so that pie crust falls over the top of the pie.

Press down on top crust gently, then crimp the edges with a fork or your fingers and cut a few slits in the top to allow steam to escape.

Brush crust all over with remaining tablespoon of cream and bake until golden brown, crust is cooked through and filling is bubbling, about 40 minutes.

Set aside to let cool for 15 minutes, then cut into slices and serve.