First we mix the room temperature butter, the granulated sugar and the dark light sugar. We can mix it by hand or with a stand mixer, until we have a smooth texture.
Add the egg and mix again.
Add the flour, salt, vanilla and baking powder and mix again until you have your cookie dough.
Incorporate the chocolate and walnuts using a spatula. You don’t need to chop the chocolate in small pieces.
Cover with film and chill into the fridge from half an hour to overnight.
Preheat your oven 356º Fahrenheit (180ºCelsius)
Form your cookies on your cookie tray with an ice cream spoon or two spoons.
Bake for 10-12 minutes, depending on your oven. If you bake two trays at the same time you will have to switch them after 5 minutes.
Let the cookies cool for some minutes before move them not to break them and let them cool over a rack.
Add some sea salt flakes and enjoy!