Knead the flour, egg yolks, icing sugar, salt, rum and milk (or sour cream) into a smooth dough, wrap in cling film, and chill for 15 minutes.
Shape the cold butter into a rectangular slab, place it on the rolled-out dough, enclose it completely with the dough, and roll out into a square.
Fold the dough in a book fold (into thirds, then into thirds again) a total of four times, chilling for 20-30 minutes between each fold, so the butter doesn't warm up.
After the last fold, rest the dough in the fridge for at least another 30 minutes.
Meanwhile make the filling: mix the curd cheese with the egg, raisins, sugar and vanilla sugar until smooth.
Roll the rested dough out to 3-4 mm thick, and with a sharp knife (dipped in hot water), cut into equal squares, about 8x8 cm.
Place a teaspoon of the curd cheese filling in the centre of each square, bring up the four corners, and pinch them together firmly in the middle so the filling doesn't leak out.
Place on a parchment-lined tray, and bake in a 200°C preheated oven for 20-25 minutes, until golden brown and the layers separate nicely.
Once cooled, dust generously with vanilla sugar and serve.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.