Quickly work the 250 g of flour together with the cold, cubed butter until you have a uniform mixture.
Shape it into a rectangle, wrap in cling film and put in the fridge for at least 30 minutes.
Knead the other 250 g of flour with the egg, the rum and just enough cold salted water to bring it together into an elastic dough.
Leave to rest covered for 10 minutes.
Roll the dough out to three times the size of the butter block, put the butter in the middle and fold the edges of the dough over it to cover it completely.
Roll it out into a rectangle, fold it in three, then rest it in the fridge for 15 minutes.
Repeat the rolling and folding twice more, resting for 15 minutes each time.
Finally roll it out 2 cm thick, cut out scones, score the tops lightly and brush with egg.
Bake in a preheated oven at 200 °C for 18-20 minutes until golden brown.
Based on: A jó házikonyha (a classic Hungarian cookbook), modernised. Calories and protein are estimated.