Combine pork knuckle, vegetables and herbs (bouquet garni) in a pot and cover with stock. Bring to boil, reduce heat, cover and cook for three hours. Let knuckle cool in the stock. Lift out and pick the meat off, discarding bones. Strain stock into clean saucepan. Bring to boil and reduce heat, reduce liquid by half. Return meat to stock, add capers, cornichons, mint, parsley, vinegar, lime zest and juice to the stock. Season. Line a 2-litre terrine tin with cling wrap. Fill with terrine mix, pressing firmly with a spoon. Cover top with cling wrap. Place a dish on top, press with weight and refrigerate overnight.