Preheat the oven to 150°C.
Toss the beef and flour in a bowl with salt and pepper.
Heat half the oil in a large casserole dish until hot.
Brown the beef in batches and set aside.
Return all beef to the pan and reduce the wine by half.
Add stock, onion, carrots, thyme, and mustard, then season.
Cover and cook in the oven for two hours.
Cool the beef mixture and remove the thyme sprigs.
Preheat the oven to 200°C for baking the pie.
Transfer beef to a pie dish and brush the rim with egg yolk.
Cover with pastry, brush with egg, and crimp the edges.
Bake for 30 minutes until the pastry is golden-brown.
Boil the green beans in salted water for 5 minutes until tender.
Drain beans and toss with butter and black pepper.
Serve a portion of pie with a side of green beans.