Put deep-frozen vegetables and 1/4 litre salt water in a pot. Cover and bring to the boil over a high heat and cook over a low heat for 8-10 minutes. Meanwhile, for the mashed potatoes, bring 1/2 litre of water and 1 level teaspoon of salt to the boil.
Take the pot from the stove, add cold milk and stir in the puree flakes briefly. Leave to stand for 1 minute, then stir again and season to taste with a little nutmeg. Peel onions and cut into rings.
Halve the slices of liver cheese. Heat 15 g fat in a frying pan and fry the Leberkäse and onions until golden brown, turning. Melt the remaining fat in a pan. Drain the vegetables and arrange on plates with the Leberkäse and mashed potatoes.
Pour melted fat over the vegetables and puree. Serve garnished with parsley. Add roasted onions as desired.