This recipe was a fusion between an old butter cookie recipe from my grandmother and a filling of azuki paste.
You can't eat just one!
It does require a little planning ahead, but it's worth it!
Mix the flour, powdered sugar and baking powder. Add the vanilla and the butter (cut in small pieces).
With a spatula, work the butter into the flour, until it all looks grainy (no more visible chunks of butter).
I always get better results when doing it by hand (perhaps the body heat helps the butter fuse with the flour).
Add the cold water and shape a ball. Do not overwork the dough! Just work it until you can form a ball and the dough doesn't crumble. If necessary, add a bit more water.
Cover the dough and let it rest for at least 10 minutes. You can also leave it in the fridge, but take it out 15 minutes before using, or it will be hard to work.
The Azuki Paste
Soak the beans in plenty of water for 10 to 12 hours.
Put the beans in a pan, cover with water, add sugar and salt and start cooking. You will have to add water as it cooks, but just enough to keep the beans covered until they are nice and tender.
Let it cook a little more (without adding water) just until you get a thick paste (enough to shape a ball).
Now, take a small piece of dough (size of a whole walnut), flatten with your hands into a small disk and put a little ball of bean paste in the middle. Close the dough around the paste and shape it all into a nice ball with a flat base (very much like the final cooked cookie)
Lay in a very lightly oiled tray and cook at 170 degrees celcius 15 to 20 minutes (don't let them brown!).
With time, you can adjust the thickness of the cookie and the amount of azuki paste you like in it.
I ran a fork on top of each cookie before cooking, just to make it look pretty!