Poppyseed cake

I've been reading a book about Eastern Europe and have become interested in itscooking, especially cakes.
This cake is made without flour, and the only hard work is whizzing the poppyseeds in a food processor or grinder, or even grinding them in a pestle and mortar.

4 eggs separated
125g butter, softened
grated rind of a lemon
100g icing sugar
2 tbspns cocoa powder
50g caster sugar
160g ground poppy seeds
 icing sugar for the top of the cake

Preheat oven 180C/gas4
Grease a 24cm round cake tin.

Beat the butter, egg yolks, lemon rind and icing sugar with an electric beater or stand mixer till thick and smooth. Fold in the cocoa and mix together.
Beat the egg whites till frothy, then sprinkle in the caster sugar and carry on beating till the whites are thick and shiny.
Mix the ground poppyseeds into the eggyolk mixture, then add the egg whites mixture and mix together very gently.
Spoon mixture into the tin.
Bake for about 55 mins. Let the cake cool in the tin.
When it's cold, take the cake out and sieve icing sugar over the top. I put a paper doily on top and sieved over this.

The cake's also nice if you ice it with a simple chocolate icing of icing sugar, boiling water and cocoa.