One of my classmates from Poland while I was attending an Italian course a couple of years ago made this and brought it to the class for us. It was oh, so incredibly delicious I had to pester the ... out of her for the recipe!!
Takes a bit of patience but technically not difficult, it is soooo good and sinful it is worth a try, I promise!! It is obviously very little known outside its native land, so here it is, one of the Poland's best kept secrets...
200g/7oz butter, cold, in small cubes
4 egg yolks
1tsp (heaped), or 1/2 sacket of baking powder
400g/14 oz your favourite kind of jam (I have tried apricot, mulberry and cactus fruit, they were all good!)
140g/5oz walnuts, roughly crushed
6 egg whites
60g/2,5oz powdered sugar
For Creamy filling
500ml/1 pint + whole milk
20g/approx. 2 tbsp flour
20g/approx. 2 tbsp corn flour(maizena)
2 egg yolks
250g/8,5 oz butter, softened
Work the butter into the flour.
Beat the yolks and the sugar together, pour and knead the mixture into the flour well.
Devide the dough in two. Roll both of them to the thickness of 5mm/0,2 inch circa.
Line 2 rectangular baking pans of the same size with wax paper. (I recommend the paper instead of greasing the pan. The handling of the crust may be a bit tricky and delicate afterwards. The presence of the wax paper is a help for a guide.)
Lay the doughs separately on each pans evenly across.
Spread the jam on top of the dough evenly, then cover with the crushed walnuts.
Whip the egg whites with powdered sugar firm, cover the surface of the dough/jam/nuts thoroughly with it.
Bake both confections for 15-20 minutes at 160°C/325°F, until the crust turns lightly golden.
Let them cool completely.
To prepare the filling, set aside a small amount of milk, enough to dissolve the cornflour(maizena) and flour,
beat these in a small vessel vigorously until the flours are dissolved.
Beat the milk, egg yolk, the flour+milk mixture and the rest of milk together, then heat the mixture in a double boiler, stirring often and thoroughly.
If you don't own a double boiler, use a thick bottomed sauce pan, use a very low heat and stir continuously.
Continue to cook, taking care not to boil it, until the mixture becomes a smooth and thick cream.
Remove from the heat, and let it cool until it becomes lukewarm.
Add the butter, mix very well until the texture becomes smooth.
Spread the filling on one of the crusts evenly. Then top with the other crust, turning over CAREFULLY so the meringue side goes in between, making a giant sandwich.
Let it chill in the fridge for a couple of hours before serving.