Peel the carrots, onions, and garlic cloves. Cut the carrots into 2-inch pieces, slice the onions, and finely chop the garlic. Cut the leek (white part) into pieces.

Wrap the bay leaves, thyme sprigs, and leek in cheesecloth or kitchen twine to form a tightly secured bouquet garni.

Place the beef pieces in a large pot with the bouquet garni, carrots, onion, and garlic. Pour in 800 ml of red wine and let marinate for at least 1 hour 30 minutes (or overnight for maximum flavor).

Take out the meat and reserve the marinade. Pat the meat dry with paper towels.

Preheat your oven to 350°F (180°C).

Heat the oil in a large Dutch oven over high heat. Sear the meat on all sides until nicely browned. Remove and set aside.

In the same pot, melt the butter, then add the flour, stirring constantly to form a roux. Gradually pour in the reserved marinade while whisking, then add the beef stock (or water). Let simmer for about 10 minutes.

Return the meat to the pot with the sauce. Add the bouquet garni and peppercorns. Cover and let simmer over low heat for about 1 hour 45 minutes to 2 hours, until the meat is tender and the sauce has reduced.

Remove the meat and keep it warm. Reduce the sauce over medium heat, then add the red currant jelly, sugar, and the remaining red wine (200 ml). Stir in the blueberries (or blackberries) for a subtle fruity note. Adjust seasoning with salt and pepper.

Place the meat in a serving dish and generously spoon the reduced sauce over it. Serve with steamed potatoes or fresh pasta for a complete meal.