Cream butter, sugar and orange zest in a medium bowl with a hand mixer until pale and fluffy.
Add egg yolk and orange water and beat until thoroughly combined.
Fold in ground and chopped almonds, flour and baking powder with a spatula and mix until well combined.
Wrap the dough in plastic wrap and refrigerate for 2 hours to chill.
Preheat oven to 315°F.
Line two baking trays with parchment paper.
Remove dough from refrigerator and shape ½ tablespoons of the dough into crescents, using lightly floured hands.
Place on prepared baking trays and bake form 12-15 minutes or until pale golden.
Cool on the baking trays for 5 minutes, then transfer to a wire rack to cool completely.
While the cookies are still warm, dust with sifted icing sugar.
Just before serving dredge heavily again with sifted icing sugar.
Store in an airtight container.