Preheat the oven to 400 degrees Fahrenheit (200 degrees Celsius).
Put a baking sheet on two baking plates.
Mix the solid ingredients: the flour, salt and baking powder.
Mix in a second bowl the butter, for about 2 minutes (untill it gets lighter). Pour the two sugars in the bowl with butter and mix for another two minutes.
Mix the vanilla and egg through the butter and lower the speed of your mixer.
Whisk the flour mixture in and mix on low speed for about 1 minute.
Add both chocolates and walnuts in the bowl and mix them in with a spatula through the batter.
Use a spoon to put a small heap of dough on the baking plate. Leave enough room between the cookies, because they will get bigger.
The baking plate goes 12 minutes in the oven.
Afterwards put the plate for about 1 minute at room temperature and use a wide spatula to move the cookies from the plate to a rack.
Cool the cookies to room temperature. In about 15 minutes the will be harden out enough to put them in your cookie basket (and I cross fingers that in your familiy the cookies will make it all the way to the basket).