In a large skillet over medium heat, melt butter. Add celery and mushrooms. Stir until vegetables begin to soften and butter starts to brown. Add chicken and onions and continue to cook, until chicken starts to heat through.
Whisk in flour, sage, rosemary, salt, pepper, thyme, chicken broth, and half and half.
Cook and whisk until no flour lumps remain. Simmer over medium-low heat until thick, about 10-15 minutes. Remove from heat and set aside.
Mix shredded Brussels sprouts, dried cranberries, diced apples, and chopped pecans into mixture.
Preheat oven to 425°F. Place the first pie dough in the bottom of the pie pan.
When the mixture has cooled, spoon into the crust, ensuring it’s even.
Cover with the second pie dough, trimming the excess and crimping the sides. Slice a few small slits in the top to allow steam to escape.
Brush the dough with egg wash and bake for about 35 minutes. Check after 20 minutes and cover the edges of the crust with foil if browning too quickly.
Brush top crust of pie with garlic herb butter once removed from the oven. Let cool for 10 minutes before slicing.
