Preparation

• Separately for each filling, mix the ingredients well. Grease well (butter is best) a square or oblong ovenproof baking dish or pan.
  
  For the strudel dough: Mix the ingredients in a bowl, knead thoroughly (ten minutes at least) and let stand to relax for one hour. Then roll out and cut into thin sheets the size of the baking container. (Alternately, purchase large sheets of strudel dough or filo pastry to suit your baking dish.)
  
  Place a layer of strudel dough / filo pastry in the bottom of the baked dish. Brush lightly with melted butter. Spread half the poppy seed filling evenly over it. Cover this layer with another sheet of strudel dough and brush the dough with melted butter. Spread this layer with half the apple filling. Cover with another sheet of dough: brush with melted butter. Spread with half the cottage cheese filling: cover with a sheet of dough, brushing with melted butter. Spread with half the walnut filling: cover with dough and brush dough with melted butter.
  
  Repeat this process with the remaining poppyseed filling, apple filling, cottage cheese filling and walnut filling, making sure to brush each layer of strudel dough with the melted butter as you proceed.
  
  Top with a final layer of strudel dough: brush with melted butter. If you like, spread this last layer with 1 cup sour cream (thinned a little with milk, if necessary, to make it easier to spread).
  
  Bake for about 1 hour in a medium oven (350F / 175C). Cut into squares and serve.