Bring the lentils to the boil in a saucepan with the meat stock, add the parsley, bay leaf and juniper berries. Season with salt and pepper.
Let the lentils simmer over low heat for about 1 hour.
In the meantime, heat the oil in a pan, roast the onions until golden, stir in the carrots and leek, roast for about 2 minutes and deglaze with the red wine. Add the whole thing to the lentils. Add vinegar to taste. Let it simmer for another 20 minutes. To taste.