Cut the hare legs in half at the joint and then cut them once more through the middle of the thigh, so you end up with three pieces from each leg.
Put the pieces into a non-metal bowl or dish with red wine, juniper berries, bay leaf, and thyme. Cover with clingfilm and refrigerate for at least 24 hours (or even 48 hours)
Drain the hare in a colander over a bowl and pat the pieces dry with some kitchen paper before seasoning the hare legs well and dusting in a bit of flour. Reserve the marinade for cooking
Heat the vegetable oil in a heavy frying pan and fry the pieces, a few at a time, until well-colored, then put to one side on a plate.
Meanwhile, in a heavy-based saucepan, gently cook the onion in the butter for 3 – 4 minutes until soft, then add the mushrooms and carrots and cook for a few more minutes more.
Add the tablespoon of flour and tomato purée, and slowly add the red wine and herbs from the marinade, stirring well to avoid lumps forming. Bring to a boil and simmer over medium heat until the liquid has reduced to half the volume.
Add the beef stock and hare, bring back to a boil, cover, and simmer gently for 1 hour (or you can cook this in an oven that has been preheated to 160°C/gas mark 3)
Remove a piece of meat to check if it's tender; if not, continue cooking for another 30 minutes or so
Once the meat is tender, remove all the pieces of meat from the sauce and set aside.
Add the blood and continue to simmer the sauce until it has thickened to a gravy-like consistency, then return the pieces of meat to warm through until it's ready to serve. Adjust the seasoning if necessary