Preheat oven to 180C/350F and prepare at least 3 baking trays with paper.
Process the nuts until they look like breadcrumbs.
Add the butter and flour to the nuts and food process again until it looks like breadcrumbs.
Add the sugar and orange rind to the food processor and let that combine.
Drop in the egg yolks a cohesive dough should form. If the dough doesn't hold a ball shape a a small amount of water.
Roll the dough into a ball and then form into a crescent shape.
The mixture makes a lot of cookies, but it can be frozen as dough or refrigerated until needed.
Bake for 12 - 15 minutes or until golden.
Dust the crescents with loads of icing sugar while they are hot. Allow the crescents to cool on the baking sheet. Dust with more icing sugar prior to serving.