Using an electric mixer, whisk together the butter and brown sugar for about 5 minutes, until white and creamy. 

Add the egg and continue mixing for another 2 minutes until combined and smooth.

In a bowl mix together the flour, baking powder, baking soda, cinnamon, salt, chocolate and walnuts.

Stir the flour-mix into the whisked butter/sugar, little by little, until just combined.

The cookie dough now needs to rest between 4-48 hours in the fridge. 

Shape the dough into a roll and wrap it in a piece of cling film.

Pre-heat the oven to 200ºC (175ºC for fan). 

Cut the cookie roll into 1cm thick slices. Leave a little space between the cookies.

If you're a fan of salty treats, sprinkle a small pinch of flaky sea salt on every cookie.

Bake the cookies for approximately 15 minutes or until golden around the edges, while still soft in the centre.