Marinate chicken in 2 cups of the white wine for at least 30 minutes and up to 24 hours in the refrigerator.
Preheat the oven to 375 degrees F.
In a large nonstick skillet, heat the oil over medium-high heat. Add the chicken and cook until the outside turns opaque, about 2 minutes. Add the onion, carrots, and celery and cook until softened, about 5 minutes. Add the mushrooms and cook for 5 minutes more.
Lower the heat to medium, add the flour and cook, stirring constantly, for 2 minutes. Stir in the chicken broth and remaining 1/2 cup wine. Stir in mustard and thyme. Let simmer, stirring often, until thickened, about 5 minutes. Add the frozen peas and season with salt and pepper, to taste. Transfer the mixture to a shallow 2-quart baking dish.
Spray each sheet of phyllo with nonstick cooking spray and layer over the baking dish, tucking the excess pastry into the dish. Bake until the filling is bubbling and the phyllo has browned, about 25 minutes. Let cool slightly before serving.
Copyright 2002, Janette Barber and Christina Deyo, all rights reserved