Bring a pan of salted water to a rolling boil and then add two whole eggs. After 6 minutes remove the eggs with a slotted spoon, plunging them into a bowl of iced water. Once the eggs are cool, peel and set aside.
Remove the sausages from their skins and mix together the meat in a bowl with the salt, mustard and chopped herbs.
Divide the sausage mixture equally (approx. 60g per egg) and cover the eggs completely and evenly. Put the flour, beaten egg and breadcrumbs into three separate bowls. Dust each egg with flour, then the beaten egg and finally coat evenly in breadcrumbs. Set aside until all the eggs have been done.
Heat the oil to approx. 160C (using a temperature thermometer) in a heavy saucepan. Note that hot oil is extremely dangerous so be careful not to overheat. Lower the eggs gently with a slotted spoon and fry for 8-10 minutes until golden and crispy. Drain on kitchen paper and serve immediately with Black Truffle Mustard.