If you're making these for Passover, make sure that your ingredients, like the powdered sugar and vanilla flavoring, are kosher for Passover. You can either buy Passover powdered sugar, or
make your own with sugar and potato starch. Similarly, you can substitute the beans of a vanilla pod (or omit the vanilla entirely) if you can't find a kosher vanilla flavoring. This recipe is adapted from
King Arthur Flour.