Drain the herb butter, sauté the spring onions, dust with flour and sweat, deglaze with water and bring to the boil while stirring constantly, add the instant powder, the cream and half of the cheese, bring to the boil again.
Grease the baking dish with the oil, layer the potatoes alternately with the Kassler slices, cover with the sauce and sprinkle the rest of the cheese on top.
Cook in the preheated oven at 175 ° on the 2nd shelf from the bottom for 30 minutes.