Put the butter in a mixing bowl. Add the icing (powdered) sugar and miso paste and beat until light in colour. Gradually add the egg yolks and mix until fully incorporated. Fold in the flour until you have a smooth homogeneous mass. Lastly, mix in the chopped walnuts.
Divide the dough evenly into 2 and place on a baking tray (sheet) lined with silicone baking pap