Peel the onion and cut it into narrow slices. Heat 20 grams of fat in a pot and fry the onion in it until golden brown. Pour pumpkin pieces with the liquid into the pot, add mustard and bring to the boil.
Add the sauce thickener while stirring and bring to the boil again briefly. Season pumpkin vegetables with mustard if necessary. Heat the oil in a pan and fry the sausages over a low to medium heat for seven to eight minutes while turning.
Meanwhile bring 1/2 litre of water and 1/2 teaspoon of salt to the boil. Add cold milk and remaining fat to the hot water. Stir in the puree flakes briefly, allow to swell for a minute and stir again with a wooden spoon.
Season with nutmeg. Wash the chives, dab dry and cut into fine rolls, except for something to garnish. Arrange sausage with pumpkin-mustard vegetables and mashed potatoes on plates. Serve sprinkled with chives and garnished.