Cut the chocolate into small pieces. Place them in a heat-proof bowl. Add heavy cream. Microwave in a 20-30 seconds interval. Take it out and stir. They won't be completely melted yet. Microwave again for another 20-30 seconds and stir. Continue doing this until only few bits of chocolate still not melted but as you stir it will melt nicely
Add the matcha powder and stir until no lumps. Let it cool down at room temperature and then cover with a plastic wrap, touching the ganache directly and then chill in the fridge for at least 1 hour or up to 3 days
For the cookie dough:
Combine all-purpose flour, almond flour, matcha powder, baking powder, salt
In another bowl, combine sugar, oil, and sugar. Whisk very vigorously for about 1 minute until sugar dissolves. Add sour cream or Greek yogurt and whisk again to combine
Add the dry ingredients into the wet and fold until they are thoroughly combined. The dough will be thick and sticky.
Cover with a plastic wrap and chill in the freezer for at least 30 minutes, or about 1 hour in the fridge. The dough is easier to work with after that. It can be stored up to 24 hours
Shaping the dough:
Position the oven racks on the upper 3rd and lower 3rd. Preheat the oven to 350 F (180 C) for conventional oven. For a convection oven, please lower the temperature by 20 F (15 C).
Line 2 large baking sheets with parchment paper. The cookies will spread so we need 2 baking sheets
If you have a #40 cookie dough scoop (medium-size). Spray with a bit of non-stick spray. Scoop about 1 1/2 Tbsp (26-30 grams) of the dough. Otherwise you can just use a tablespoon to do this
Lightly oil your palms and roll it into round dough ball. Place the dough ball on the prepared baking pan, about 2 inches apart, about 12 dough balls per baking pan. Continue with the rest of the cookie dough
Baking:
Bake in the preheated oven for 15 minutes, rotate halfway, front to back, top to bottom halfway through baking time
The top of the cookies will crackle. Remove from the oven and let them cool completely on the rack
Assembling:
The ganache will be firm after being in the fridge. Let it sit at room temperature a bit and then stir it to soften. Roughly portion it into 12 equal portions the best you can, then roughly shape it into a dollop
Place 12 cookies, flat side up. Place the ganache on the center.
Top with another cookie and gently press to spread the ganache. You just make one cookie sandwich. Repeat with the rest of the cookies and ganache filling.
How to store:
Store them in an air-tight container and keep them chilled in the fridge for 3-4 days. Place a piece of parchment paper in between if you plan to stack them. Let them sit at room temperature for about 30 minutes before eating for the best texture
They also freeze very well. Freeze them in a single layer on a baking sheet for about 1 hour. Then wrap each one with a cling wrap and put inside a freezer bag, push all the air out and seal
Simply thaw overnight in the fridge or at room temperature and then let them sit at room temperature for about 30 minutes or so before eating. You can also thaw at room temperature for a few hours before serving