Lightly toast walnuts in an oven at 170°C for about 7 minutes. Or you can fry (without oil) in a frying pan for a few minutes. Let it cool down and chop finely.
Add flour, butter, walnuts, salt, sugar and vanilla extract in a bowl and mix everything well together (using hands).
Gather together all the ingredients into a dough and wrap in a plastic bag. Refrigerate for about 30 minutes so it is easier to handle.
Remove dough from the plastic bag. Pinch some dough and roll it into 1 inch balls.
Line a tray with baking paper and arrange cookie balls about an inch apart from each other.
Bake in an oven (no fan) at 175°C until golden brown, about 15 minutes.
Remove the tray from the oven and let it stand for about 3 minutes.
Sift powdered sugar onto a bowl and roll each cookie ball gently until coated with the sugar.
Leave to cool for about 20 minutes and roll again gently in the powdered sugar.
Notes
I find that the cookies taste better if they are baked till golden brown all round.