Grind walnuts in the food processor.

I a large bowl combine walnuts, flour, baking powder, powdered sugar and cinnamon. Mix together. Add egg yolks. Cut butter into small pieces or shred them. Add to the flour. Combine all ingredients well. Form a ball. Cover with foil. Place the dough in the fridge for 30 minutes.

In the meantime, in a large pan melt 4 Tbsp. butter, add apples and cook on low-medium heat for 10 minutes. When apples will be soft add cinnamon and brown sugar. Cook for another 5 minutes.

Preheat oven to 350 F. Prepare 13 x 9 baking pan with parchment paper.

In a medium bowl beat the egg whites until soft peak, add sugar gradually (about 3 times). Mix ingredients well. Add lemon juice and mix.

Remove the dough from the fridge and cut about 3/4 dough. Leave the rest for the top.

Spread 3/4 dough on the bottom of the baking pan nicely. Add apples.

Add egg whites.

In the end shred the remaining dough and spread on the top of the apples.

Bake for about 50 minutes.