To serve:
Cut the venison into 3–4cm chunks and place in a stainless steel or ceramic bowl with the red wine, garlic, thyme, bay leaf and juniper berries. Cover and leave to marinate in the fridge for 2 days.
Drain the meat in a colander, reserving the marinade, and dry the pieces on some kitchen paper. Flour the meat lightly, using a tablespoon of the flour, and season with salt and pepper. Heat 2 tablespoons oil in a heavy-based frying pan and fry the meat, a few pieces at a time, over a high heat until nicely browned.
Heat the butter in a large, heavy-based saucepan and gently fry the onions for a few minutes until soft. Add the remaining 2 tablespoons flour and the tomato purée, and stir over a low heat for a minute. Slowly add the reserved marinade, stirring constantly to avoid lumps forming. Bring to the boil and simmer until it has reduced by half.
Add the beef stock and the pieces of venison and bring back to a simmer. Cover with a lid and simmer very gently over a low heat for about 1 ½ hours until the meat is tender. It's difficult to put an exact time on braising meat; you may find it needs an extra half an hour. Once the meat is cooked, the sauce should have thickened sufficiently. If not, mix 1–2 teaspoons cornflour with a little cold water, stir into the sauce and simmer, stirring, for a few minutes.
Meanwhile, put the carrots in a pan and just cover with water. Add the butter, sugar and seasoning and simmer rapidly until the carrots are tender. Drain off any excess cooking liquid, leaving a little to glaze them, then toss with the chopped parsley.
Divide the stew among warm bowls and top with the glazed carrots. Serve at once.