Preheat oven to 400˚F.
Heat EVOO in a large skillet or Dutch oven over medium-high heat. Add chicken and brown 7-8 minutes then remove to plate.
Add butter and melt. Add apples, celery, onion, bay, thyme, salt and pepper, and cook to soften, 8-10 minutes. Sprinkle with flour, stir 1 minute then whisk in cider and stock. Slide chicken back into pan and simmer a few minutes to thicken sauce.
Place in casserole dish or individual casserole dishes arranged on baking sheet to catch drips. Cover with pastry, brush with egg wash and bake until golden.