Preheat the oven to 350°F and place a rack in the center.
Grease a 9-by-9-inch baking pan, or line it with parchment paper.
In a stand mixer fitted with the paddle attachment, beat the butter, sugar, and miso until well incorporated and fluffy, about 2 minutes. Scrape down the sides of the bowl as needed. Add the flour and matcha and mix on medium-low speed until a dough forms. Fold the pistachios into the dough until evenly distributed.
Transfer the shortbread dough to the prepared pan. Using the back of a spoon or clean fingers, firmly press the mixture evenly over the bottom of the pan, covering all edges and the sides. Use a fork to poke holes across the entire surface of the dough.
Bake 15 minutes, until lightly browned and puffy. Remove from the oven and let cool 10 minutes. Cover and refrigerate 30 minutes.
Meanwhile, make the berry cream: Combine water and gelatin in a bowl. Let the gelatin bloom for a few minutes, then microwave 10 seconds, until melted.
In a large bowl, add the coconut milk, condensed milk or honey, miso, jam, lemon zest or juice, and optional food coloring, and whisk until homogeneous. Stir in the melted gelatin and mix until combined. Fold in the optional dried cranberries. Take the pan out of the refrigerator. Pour the berry cream on top of the shortbread. Tap gently against the counter and smooth out the top with a spatula.
Cover and refrigerate at least 4 hours or overnight.
Cut into 12–16 even pieces. Garnish with the optional toppings. Enjoy!
Refrigerate leftovers and consume within a few days.