Fry the bacon lardons in 15ml of oil until crisp and set aside.
Dust chicken in seasoned flour and brown in the pan for three minutes.
Sauté sliced onions in the remaining oil for five minutes while scraping the pan bottom.
Return bacon, chicken, and remaining flour to the pan and cook for five minutes.
Add wine, stock, and thyme, then simmer for 30 minutes.
Stir in butter beans and simmer for a further 10 minutes.
Allow the mixture to cool completely before removing meat from the bones.
Transfer meat and sauce to a 25x20cm dish and dot with butter.
Preheat the oven to 200°C.
Cover dish with rolled-out pastry, crimp edges, brush with egg, and cut a steam hole.
Bake for 25 minutes until the pastry is golden and crisp.