Soak poopy seeds in the milk and vanilla overnight.
Cream butter until soft. Add the sugar gradually and cream well. Sift the flour, baking powder and salt together. Blend the flour and poppy-seed mixtures alternately into the creamed butter mix. Blend well.
Whip the egg whites until stiff and fold into mixture.
Pour the batter into 2 buttered and lightly floured 8" layer cake tines, and bake 30 minutes in a preheated 350° oven. Let cool a little in the pans before turning out onto racks. If you wish you can cut each layer in half and spread filling between four layers. Whichever you choose to do, here's a suggestion for a mouth-watering between-the-layers spread:
Beat the egg yolks until frothy. Mix sugar, cornstarch, milk and salt with the beaten yolks and cook in the top of a double boiler over hot water about 5 minutes. Stir constantly to keep the mixture from scorching.
Grind nuts and add to cooked mixture with vanilla. Mix well, and spread between layers.
Top the cake as follows:
Stir the sugar with the rum until smooth. Add the water and beat well. Ice the sides and top of the cake. Sprinkle the ground nuts over the top.