Make sure you weigh all the ingredients (even the egg whites), instead of using cups and teaspoons as measurement. Those are less precise than weight measurements, and precision is super important with these cookies.
In a food processor, combine the almond flour, confectioner's sugar, and matcha powder. Grind together until it's a fine, incorporated powder.
Sift into a large bowl (if there's a lot of material left, then grind again, and keep sifting).
In a silver mixing bowl, begin whipping the egg whites and cream of tartar, starting on low speed and gradually increasing.
Slowly pour in the granulated sugar, allowing them to incorporate together.
If you'd like your macarons to be more green than they will be with matcha only, put a couple drops of green gel food coloring in the mix (not liquid coloring -- gel only). I like the light green color, so it's up to you.
Once the egg whites form stiff peaks, put the dry ingredients in and fold them, until they are just incorporated, and there are no streaks left. But don't over-fold. It's a delicate balance.
Transfer to a piping bag and pipe out little 1/2-inch circles (with about an inch between them) either on parchment paper or a silicone baking mat.*
Once they're all piped out, smack the cookie sheet onto your counter a few times to get rid of any air bubbles in the cookies, then leave the cookies out on the counter for about 20 minutes, until the cookies have a bit of a crust.**
Preheat the oven to 350 degrees (F). ***
Once cookies have formed their crust, cook for 10 - 12 minutes, watching not to over-bake. (Be careful of altitude--if you're at higher altitude, the air is thinner, so that affects your baking time.) Take out the cookies and let them cool. Do not fill before they're completely cool.
Whip the butter in a standing mixer until it's creamy.
Add the confectioner's sugar slowly, until it's thick, then add the sour cream.
Add the grated ginger, cardamom, and cinnamon. Mix until incorporated.
Stir in the crystallized ginger.
Pipe the filling into the center of the cookies and sandwich them together, check for size fit with each cookie.
Eat and enjoy!
*I like a variety of sizes so made large (up to 1-1/2"), medium, and small-sized cookies. For the larger cookies I added 1 - 2 minutes extra baking time.
**If you live in a humid environment, it may take longer for the cookie to develop a crust. I've had it take close to an hour with other recipes on hot summer days, but be patient. The "crust" is what keeps the cookie top from cracking during baking. If the crust has developed properly, the cookie should not feel sticky when touched.
***You don't want these cookies to brown, so I would recommend baking at 325 degrees (F).
After the cookies have baked, remove the parchment paper (with the cookies still attached) to a wire rack to cool completely before filling.
Store leftovers in an airtight container in the refrigerator. I thought the cookies were still very good the following day, after the flavors had melded together.
I took the liberty of adapting the author's ginger buttercream recipe by only making half the original but adding additional confectioners' sugar to make it thicker. The filling recipe above is the one that I made and proved to be sufficient to generously fill the macarons.
https://cinnamonsugarandalittlebitofmurder.com