Cook the potatoes in boiling salted water for 10-12 minutes or until soft.
Heat the sunflower oil in a heavy-based saucepan. Add the onion and cook until soft , but not coloured. Stir in the mustard then pour in the stock. Bring the mixture to the boil, then add the gravy browning. Reduce for 10 minutes or until the liquid is reduced by half.
Heat up a frying pan, add a little sunflower oil and fry the sausages for 6-8 minutes or until cooked through.
Drain the potatoes and mash with the butter and the cream. Blend the blanched herbs with the olive oil to form a paste and then stir into the mashed potato.
Pile the mash onto four warmed serving plates. Place two sausages in the centre of each mound of mash and finally drizzle over the gravy.