Preheat oven to 400°
For the Filling:
In a large skillet, melt butter, sprinkle flour over butter and mix until smooth; cook 1 minute. Stir in broth and cream. Simmer until thickened. Add poultry seasoning, salt, pepper, onion, carrots and mushrooms. Turn down heat and cook until vegetables are tender (about 2 minutes). Stir in peas and chicken (about 2 1/2 cups).
For the Crust:
Press 5 biscuits in the bottom and up the sides to the top of a 2 quart baking dish. Pour prepared filling on top of bottom crust. Roll remaining 5 biscuits large enough to hang over the top of the baking dish. In a small bowl whisk together the egg yolk and water. Brush to top of the bottom crust, add the top crust, fold the top crust over the bottom crust to create a seal and crimp. Brush the top crust with the egg wash. If you want, add a sprinkle of salt and pepper.
Cover with foil and bake 10 minutes, remove foil and continue baking for 20 minutes or until the crust is golden brown.