Place the cream in a medium microwave-safe bowl and heat in 30-second intervals, stirring after each, until the cream is hot and begins to bubble slightly. The total time may vary depending on your microwave.

Remove from the microwave and add the chocolate. Stir until completely melted and smooth. If needed, microwave in additional 10-second bursts, stirring after each until fully combined.

Let the ganache come to room temperature, about 30 minutes.

In a large bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.

Using a handheld or stand mixer fitted with a paddle attachment, beat the butter, granulated sugar, and brown sugar on medium-high speed for about 3 minutes, until creamy and fully combined. Scrape down the sides and bottom of the bowl as needed.

Beat in the egg and vanilla extract until fully incorporated.

Gradually add the dry ingredients to the wet mixture, mixing on low speed until a thick dough forms.

Line large baking sheets with parchment paper or silicone baking mats. Roll the dough into small balls, about 1 tablespoon cookie scoop or 30g each, and place them on the prepared baking sheets. Flatten each ball into discs about 1.5 inches in diameter, using the flat bottom of a measuring cup or drinking cup. Be sure to keep the size consistent for even sandwiching later.

Place the baking sheet(s) in the refrigerator for 15 minutes to help the cookies hold their shape during baking.

While the dough chills, preheat your oven to 350°F (177°C).

After chilling, space the cold, flattened cookies about 3 inches apart on the baking sheets. You’ll need to bake in batches, so keep the remaining cookies in the fridge while the first batch bakes.

Bake for 8–10 minutes, or until the edges are set and the tops begin to crack slightly.

Remove from the oven and let the cookies cool on the baking sheets for at least 5 minutes before transferring them to a wire rack to cool completely.

Once the cookies are completely cooled, spread or pipe the ganache onto the bottom sides of half of the cookies. If using a piping bag, I recommend Wilton tip #12 for even distribution.

Sandwich the remaining unfrosted cookies on top of the ganache filling, pressing down gently to secure.

Optional: Drizzle extra ganache over the top of each sandwich cookie and sprinkle with flaky salt for added flavor and texture. Highly recommended!