Roast the onions in a pan. Add the minced meat and roast well. Then add the leek, mushroom slices and white cabbage and cook a little. Season well with salt, pepper and soy sauce and allow to cool. Add the egg yolks and grated cheese and mix well.
Pour the mixture onto the rolled out puff pastry, fold in the pastry and press the edges into place. Brush the strudel with egg white.
Bake in the preheated oven at 200 ° C for about 30 minutes.