In a large bowl, combine dough ingredients & knead until smooth. Wrap in plastic wrap & place in refrigerator for at least 1 hour or overnight.
Poppy Seed Filling
In a small saucepan, combine all poppy seed ingredients. Place over LOW heat for 1-2 minutes; remove from heat & cool.
In a small bowl, combine all nut filling ingredients; set aside.
In a small saucepan, saute peeled & chopped apples over low heat with butter & sugar. Do not add any water as they need to be semi-soft, NOT MUSHY.
Assembly of Cake
Divide chilled dough in HALF, then divide one of the halves into THIRDS. Roll out the largest piece into a circle big enough to cover the bottom & sides of a 12-inch spring form pan. Make sure to have a bit hanging over the top of the ring.
Add the poppy filling. Roll out one of the small pieces of dough to fit neatly on top of filling. Gently cover with nut filling. Roll second small piece of dough; fit over nut filling. Add apple filling layer. Fold extra dough edges onto apples & top with third piece of dough. Your dough base & dividers should all be rolled quite THIN.
Preheat oven to 350 F. Beat egg & add a tiny bit of water. Brush it over top surface. Bake for about 1 hour & 20 minutes until golden. Remove from oven & place on a wire rack to cool. This cake is best if left in a cool place for a day or two before serving so the flavors will marry. Dust with a layer of powdered sugar before serving.
When you’re making this type of cake, never hesitate to adjust the quantity of any one of the filling layers to make it not as thick if you feel it might be too overpowering to your personal taste.