Beat the 2 egg whites with the powdered sugar and the lemon juice until foamy.
Whip the 5 egg whites into a stiff foam, and fold slowly into the sugar-lemon base, then sprinkle in the breadcrumbs and fold in gently.
Butter and flour a lidded pudding mold, pour in the foam mixture, and put on the lid.
Pour enough hot water into a larger pot so the mold sinks in about two fingers deep; cover the pot too, and steam over low heat for about 45 minutes.
Turn the finished pudding out onto a plate, and chill (in the refrigerator for at least 1-2 hours).
For the custard, whisk the egg yolks with the sugar and the split vanilla pod in a bowl over a water bath until fluffy, then pour in the milk.
Standing the bowl in hot water, cook, whisking constantly, into a thick cream (about 8-10 minutes, until it coats the back of the whisk); then set in cold water to cool, stir in the rum, and chill.
To serve, whip the cream stiff, fold in the sugar and a few drops of red food coloring, pipe it decoratively onto the chilled pudding, and serve surrounded with the vanilla-rum custard.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.