Make a four-fold puff pastry from the butter and flour (or use shop-bought puff pastry), roll out to the thickness of a knife-back, and line a buttered mold with it.
Mix the egg yolks smooth with the sour cream.
Add the ground leftover meat, season with salt and pepper, then mix in the wilted mushrooms, the onion and the parsley.
Carefully fold in the whipped whites of the 4 eggs.
Pour the mixture into the lined mold.
Bake in a preheated oven at 180°C for 45 minutes, until the top is a nice golden brown and the center is cooked through.
Turn out of the mold, and serve warm.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.