Warm the cream over low heat, stirring constantly, until lukewarm (do not let it boil), then set aside.
Proof the yeast in the 50 ml milk with the half sugar cube and a little flour: leave in a warm place for 10 minutes until foamy.
Mix the egg yolks, sugar, salt and the proofed yeast into the lukewarm cream.
Put the flour in a warm bowl, pour in the cream mixture and the rum, then quickly and vigorously work it with a wooden spoon until you get a smooth, elastic dough, similar in texture to the Carnival doughnuts.
Cover and leave to rise in a warm place for 45-60 minutes, until doubled.
Turn out onto a floured surface, flatten to about 2 cm thick, cut out rounds with a doughnut cutter, then let rise again on a floured tea towel for about 30 minutes.
Fry in 170°C oil/lard, starting covered, then uncovered, until both sides are golden.
Drain on paper towels and serve warm, dusted with icing sugar.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.