Step 1. Add flour and cubed cold butter to a bowl. Cut the butter into the flour until the mixture resembles coarse crumbs.

Step 2. Add the rest of the ingredients and knead lightly by hand. Do not over knead as the dough will harden.

Step 3. Divide dough into two, with the half used for the bottom layer slightly larger than the other. Refrigerate for one hour.

Step 4. Roll out bottom layer (without flour) and place in pan, making sure that the dough comes up the sides slightly. Prick the dough evenly with a fork to prevent air bubbles from forming.

Step 5. Roast walnuts and ground them. Place ground walnuts over bottom layer. Add the cinnamon and lemon zest.

Step 6. Squeeze the grated apples to remove excess liquid. Place over bottom layer and sprinkle with sugar and cinnamon.

Step 7. Roll out top layer and place over apples. Brush the dough with beaten egg yolk for a golden crust.

Step 8. Bake at 335 degrees for 50 minutes. Cool and cut into squares after sprinkling powdered sugar over it. Enjoy!