Heat oven to 140C/fan 120C/gas 1. Cut the base of the garlic bulb so that the cloves are just showing, then wrap lightly in foil. Bake for 1 hr until completely tender, then leave until cool enough to handle and squeeze the flesh into a bowl - you should have about 2 tbsp. Cover and set aside.
Heat 1 tbsp oil in a shallow casserole or heavy-based pan with a lid. Cook the beef in batches over a medium heat for 3-4 mins until evenly browned, then tip on to a plate. Using the rest of the oil, repeat until all of the beef has browned. Add the onion and thyme to the pan then cook for about 5 mins until softened. Stir in the mustard and cook for 1 min. Pour the red wine into the pan and cook for a few mins until well reduced and syrupy.
Return the beef to the pan, add the carrot, then pour in the stock. Bring to the boil, stirring, then reduce the heat and simmer gently with the lid on for 1½ hrs or until the beef is tender and the sauce has slightly reduced and thickened. Spoon into a 2 litre/3½ pint pie dish and leave to cool completely.
Increase oven temperature to 180C/fan 160C/gas 4. Simmer the potatoes in a pan of boiling salted water, for 15-20 mins or until tender. Drain, then mash with the reserved garlic, butter, milk and parsley. Season to taste, then carefully spread over the beef to cover completely and fl uff up with a fork. Bake for 25- 30 mins until heated through and lightly golden. Serve the pie straight away.
To prepare ahead, assemble the pie and freeze for up to a month, or refrigerate
for up to 2 days.