Drop the duck eggs into boiling water. Cook for 7 minutes, then rinse under cold water and leave in cold water for 10 minutes to cool completely. Peel.
Strip the skins from the sausages, then mix with the sage and parsley and season well. Divide the mixture into 4, then flatten each into a circle on 4 pieces of cling film. This will make it easier to form around the eggs.
Dust the peeled eggs with flour then sit each on the sausage meat. Use the cling film to mould the sausage meat around each egg, ensuring there are no gaps.
Roll each egg in flour, then the beaten egg, then breadcrumbs. Repeat with the beaten egg and breadcrumbs. Chill until ready to cook.
Heat groundnut oil, no more than 1/3 deep in a pan, to 180°C Cook the eggs for 5-6 minutes, turning a few times until golden and crisp. Serve with brown sauce or ketchup.