Peel 16 medium potatoes (for 4 servings) and cut into cubes. Put all the vegetables and season with salt and pepper. Prepare 4 sheets of foil so that they fit and you can wrap vegetables and veal. Brush each piece with butter. Spread the vegetable mixture: potatoes, onions, leeks, tomatoes, carrots, put a clove of garlic, a sprig of rosemary and thyme on top.