1. In a large pot, boil the russet potatoes over medium heat for 10-15 minutes or until potatoes have softened.
2. In a saucepan, heat the vegetable oil over medium heat and sautee in the chopped onions until soft, but not coloured. Stir in the mustard and then pour in the beef stock. You may use chicken stock instead if you want.
3. Bring the mixture to a boil, then reduce to a simmer for 10 minutes or until the gravy has thickened. Add in salt and pepper, mix well. For extra flavour, you may add in rosemary to the gravy while it is simmering.
4. Next, in another frying pan, add a little vegetable oil and fry up the sausages until cooked through.
5. Drain the cooked potatoes in a colander, then mash it in a bowl. Add in butter, cream, salt and mix well with a wooden spoon. To get fluffy mash, stir the mash vigorously until light and fluffy. Toss in the parsley and chives until evenly mixed.
6. Then, to serve, Place mash potatoes onto individual plates, arrange the sausages onto the mash mounds and pour over the gravy.Garnish with the chopped spring onions. Serve hot.