First, grind the walnuts in a blender or food processor until they turn into a coarse flour consistency. Some bigger bits are fine, but make sure you don't process them too much or the walnuts will turn into a sticky mass.
In a mixing bowl, beat the butter and sugar with a hand mixer until smooth and creamy. Mix in the vanilla extract.
Add the flour and mix it in. Finally, add the ground walnuts and stir to combine into a soft, sticky dough.
Use a cookie scoop (recommended) or your hands to form 10 to 12 equal sized portions of the dough, placing them 1 inch apart on a baking tray lined with a silicone mat or non-stick baking paper.
Place the tray in the fridge and chill for 30 minutes. Chilling is mandatory to ensure the cookies retain their shape.
When ready to bake, preheat the oven to 175 C. Slide the tray into the oven and bake for 15 to 20 mins until the bottoms have flattened a little bit, and the tops and edges are lightly browned.
Set aside to cool for 5 mins. Spread the sifted, powdered sugar out onto a large, flat plate and roll the still-hot cookies in it, coating them all over. Transfer to a wire wrack to cool completely, then roll one more time and eat the whole batch!
These cookies taste best fresh in my opinion but can be stored at room temperature in an airtight tin for 4 to 5 days, or frozen. Happy baking and happy Christmas!