Growing up this was my favorite cookie from the wide selection of typical German christmas cookies. They are buttery, tender, and melt in your mouth. I have been making these for years, I can't really say were the original recipe came from, but it's probably common knowledge of German bakers. Instead of rolling them in icing sugar you can use very fine granulated sugar, both versions are good. This recipe just makes one tray of cookies, it can be easily doubled if you need more. You should bake them one tray at a time, so you manage to do the sugar-rolling while they are still hot. The vanilla sugar is plenty for the amount of cookies, but you can just keep the rest for the next batch! —Yoolie
Sieve the icing sugar into a lidded container. Scrape the seeds from the vanilla beans. Add about half the seeds to the icing sugar, reserve the rest. Put both empty vanilla beans in the container with the sugar, close and shake well. Leave to infuse for a while (the longer the better!).
In a large bowl, mix together flour, almond flour, sugar, butter, the other half of the vanilla seeds and a pinch of salt. Use your hands and work the dough until everything is incorporated. Then roll the dough into a stick (about 1 inch in diameter), wrap in cling foil and put in the fridge for at least 30 minutes.
Preheat you oven 375° F. Cover a baking tray with parchment paper. Cut the dough-roll into 1/2 inch-slices. Then form them into "kipferl", little crescend-moon shapes. Place on the baking tray and bake for about 20 minutes. The cookies are done when they begin to brown around the edges.
Let the cookies cool on the tray for about 3 minutes. Then roll them carefully in the vanilla icing sugar. The kipferl should be covered in sugar from all sides. When they are completely cooled, put them in a tin cookie jar and cover with more sugar. Like that they should keep for about three weeks (though they tend to vanish a lot quicker in my house).