Preheat the oven to 350F.

In a bowl, add butter, sugar and lemon zest and whisk until its smooth. If you are using the stand mixture, use the paddle attachment.

Drop the eggs and whisk until its smooth.

In a separate bowl, whisk the dry ingredients (flour, cocoa powder and salt).

Add the dry ingredients to the bowl with wet ingredients and whisk until it forms a dough. Do not over mix it.

Finally, drop the walnuts and using a rubber spatula, mix it with the dough.

Place the dough on a baking tray and shape it like a 2-inch wide log.

Place the tray on the middle rack of the oven and bake for 35 minutes.

After 35 minutes, take out the tray and place the baked log on a wire rack for 20 to 30 minutes or until it’s cooled down completely and easy to handle.

Preheat the oven once again to 350F.

Using a sharp serrated knife, cut the log carefully into ½ inch thick slices.

Place the slices on the baking tray and bake it at 350F for 10 minutes and then flip the cookies. Continue baking for another 10 minutes.

Once done, cool the cookies on the wire rack before storing it in an airtight jar.