Peel and wash the potatoes and cook them in boiling salted water for 20-25 minutes. Wash and peel asparagus, cut off woody ends. Boil up plenty of water with 1-2 teaspoons of salt, about 1 teaspoon of sugar and 1 teaspoon of lemon juice in a large pot.
Cook the asparagus for about 15 minutes. Wash the meat, dab dry and if necessary tap it thinner between 2 layers of foil. Fill cornflakes into a freezer bag and crumble finely. Mix crumbs with breadcrumbs.
Season meat with salt and pepper. Beat the egg and milk. First roll the meat in flour, whisked egg and then in cornflake breading. Heat oil in a frying pan in portions, fry escalopes in it in portions on each side for about 3 minutes until crispy brown.
Remove the finished cutlets, drain them on kitchen paper and keep them warm. Melt 100 g butter. Beat egg yolks, 1 tbsp. lemon juice and white wine over a hot water bath until frothy. Gradually fold in liquid butter and yoghurt.
Season to taste with 1 tablespoon lemon juice, sugar, salt and pepper. Wash parsley and dab dry. Pluck off the leaves and cut finely. Drain potatoes and mix with 1 tbsp. butter and parsley.
Arrange schnitzel, potatoes and asparagus on plates. Serve with yoghurt-Hollandaise. Garnish with lemon slices.