Beat the butter until fluffy, then add the 2 whole eggs and 3 egg yolks one at a time, mixing thoroughly after each.
Add the ground almonds, grated chocolate, breadcrumbs, sugar, slivered almonds and lemon zest, and mix until smooth.
Whisk the egg whites to stiff peaks, and gently fold into the mixture.
Grease a clean tea towel with butter, spoon the mixture onto it, and roll up tightly into an even log shape, tying both ends and the length with kitchen string to hold its shape.
Bring a large pot of water to the boil, add the wrapped log, and simmer gently (not boiling hard) for about 45 minutes, turning it once.
Lift out of the water, let cool for a few minutes, then unwrap from the cloth.
Make the wine custard: whisk the egg yolks, sugar, wine and lemon zest together over a bain-marie, beating continuously with a whisk, until it becomes a thick, foamy cream, about 8-10 minutes, without letting it boil.
Slice the log, arrange on a plate, and serve at once with the warm wine custard.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.