Whisk together the flour, cocoa powder, and salt in a medium bowl and set aside. In a stand mixer, cream the softened butter with both the granulated sugar and packed brown sugar until light and fluffy, about 3-4 minutes, scraping down the sides halfway through. Add the room temperature eggs one at a time, scraping down the sides after each addition to ensure even incorporation. Add the dry ingredient mixture from the flour mixture and mix on low speed until the dough just comes together and is smooth. Divide the dough in half, shape each into a flat disc, wrap tightly in plastic wrap, and refrigerate for at least 4 hours or overnight—this resting time is crucial for preventing the dough from spreading too much during baking.
While the dough chills, place the 14.8 oz of chopped white chocolate in a medium heatproof bowl. In a small saucepan, combine the 1 oz unsalted butter, corn syrup, and cold heavy whipping cream, then heat over medium heat until the mixture is steaming and the butter is fully melted. Pour the hot cream mixture over the white chocolate and let it sit undisturbed for 1-2 minutes to allow the residual heat to soften the chocolate. Stir gently until completely smooth, then whisk in the kirsch cherry liqueur. Cover the ganache with plastic wrap and set aside to cool to room temperature—the ganache will thicken as it cools and is essential for the cookie sandwiches.
Preheat your oven to 350°F and line two baking sheets with parchment paper. Working with one disc of chilled dough at a time, place it between two sheets of wax paper and roll to an even thickness of 1/8 to 1/4 inch. Cut out your desired shapes using cookie cutters—you'll need pairs of cookies, so cut half of each batch with a small center cutout (these become the top cookies). Freeze the cut cookies on the baking sheet for a few minutes to firm them up, which prevents distortion during baking. Bake for 9 minutes until the cookies are set but still slightly soft to the touch, then cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely. I find that slightly underbaking these keeps them tender enough that they won't crack when pressed together with the ganache.
In a small microwave-safe bowl, combine the 5.3 oz finely chopped white chocolate with the coconut oil and microwave in 20-second intervals, stirring between each, until completely melted and smooth. Drizzle this white chocolate mixture over the top cookies (those with the center cutouts) using a fork or squeeze bottle to create an elegant pattern. Using a microplane grater or vegetable peeler, shave the dark chocolate bar and gently sprinkle the shavings over the wet white chocolate while it's still set. Freeze these decorated top cookies for 5-10 minutes until the white chocolate coating is completely set and firm.
Transfer the cooled ganache from Step 2 to a piping bag fitted with a small round tip. On the flat bottom side of the undecorated cookies (those without cutouts), pipe a thin ring of ganache around the outer edge, leaving the center open. Spoon about 1 teaspoon of sour cherry preserves into the center of each ganache ring on the bottom cookies. Take the decorated top cookies from Step 4 and carefully press them ganache-side down onto the bottom cookies, pressing gently so the ganache and preserves create a seal without squeezing out excessively. I like to work with one cookie sandwich at a time to ensure the ganache is still pliable and creates a good bond. Place the assembled cookies on a baking sheet and freeze for at least 15 minutes to ensure the ganache sets and holds the sandwich together firmly.
