Melt the butter until foamy, add the flour, and stir into a smooth, thin roux.
Add the cold milk, and cook into a thick béchamel paste, stirring constantly.
Once cooled, mix in the 4 egg yolks and the salt, then gently fold in the whipped whites of the 4 eggs.
Grease and flour a rimless baking sheet, spread the mixture onto it in a layer the thickness of a little finger, or even thinner, and bake in a preheated oven at 180°C for about 15-20 minutes, until set.
Let it cool a little, then cut cutlet shapes (oval or round slices) out of the sheet.
Mix the ham with the sour cream, and sandwich two slices together with this filling.
Roll the pairs in egg, then breadcrumbs.
Fry in hot lard or oil until golden brown on both sides, and serve hot.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.