Preheat your oven to 180 degrees Celsius (350 degrees Fahrenheit), and line two baking trays with baking paper.

In a large bowl, cream the butter and sugars together using an electric mixer until light and fluffy. Add eggs one at a time, and beat until combined.

To the mixture add flour, salt, baking powder and baking soda, and mix until fully incorporated.

Fold in the chocolate chips and walnuts gently with a wooden spoon.

Transfer the dough onto a clean surface and mix by hand to evenly distribute the ingredients. The dough should be stiff enough to form cookies. Divide into 12 equal portions and place on the baking trays.

Chill the dough balls in the fridge for about an hour, and then bake for 15 -20 minutes, depending on how you like the middle. The cookies should be lightly browned when you get them out of the oven.

Let the cookies cool on a rack and serve warm. These will last for a few days in an airtight container, if they manage to not get demolished beforehand.