The chocolate ganache needs at least 45 minutes to thicken before it can be used in the cookie sandwiches. I recommend starting the ganache while the cookies are in the oven.

Make the cookies: In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium-high speed until smooth and creamy, about 2 minutes. Add the confectioners’ sugar and orange zest, and beat until completely combined. Scrape down the sides and bottom of the bowl as needed. Add the egg, egg yolk, vanilla extract, and salt. Beat on medium-high speed until combined, scraping down the sides and bottom of the bowl as needed. Finally, add the flour and beat on low speed until incorporated, then gradually increase the speed until the dough comes together. The cookie dough will be very, very soft.

Generously flour a rolling pin. Roll out the dough onto a very generously floured sheet of parchment paper or a silicone baking mat (I prefer the silicone mat) to about 1/4-inch thickness. The rolled-out dough can be any shape, as long as it is evenly 1/4-inch thick. Sprinkle with more flour as needed to prevent sticking. (If it helps, place a piece of parchment on top of the dough before you roll it out, to keep the rolling pin from sticking to the dough.)

Place the rolled-out dough, with the parchment or mat underneath, onto a baking sheet and refrigerate for at least 3 hours and up to 2 days. If chilling for longer than a couple hours, lightly cover with parchment paper or plastic wrap.

Preheat the oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats.

Remove the dough from the refrigerator. Using a 1.5-inch round cookie cutter, cut into shapes. I used the 1.5-inch fluted round cookie cutter from this set. Re-roll the dough scraps and continue cutting until all is used. Arrange cookies on baking sheets 2 inches apart. If desired, sprinkle and lightly press some coarse sugar into the tops.

Bake cookies for 9–11 minutes until very lightly browned around the edges. The cookies do not brown much on top. Rotate the baking sheets halfway through bake time.

Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a cooling rack to cool completely before filling.

Make the ganache: Place chopped chocolate in a heat-safe bowl. Heat the cream in a small saucepan until it begins to gently simmer. (Do not let it come to a rapid boil—that’s too hot!) Pour over chocolate and let it sit for 2–3 minutes to gently soften the chocolate. Slowly stir until chocolate is completely melted and combined with the cream. Allow to cool and thicken until it’s a pipeable/spreadable consistency, at least 45 minutes, or up to 1.5 hours (depending on the temperature of your kitchen).

Fit a piping bag with a large round tip, such as Wilton #12. (You can spread the ganache on with a knife if you don’t want to use a piping tip, but it can get pretty messy!) Fill the piping bag with the thickened ganache. Flip half of the cookies over and pipe a dollop of ganache onto the flat side. Top with the remaining cookies and gently press until the ganache spreads to the edges.

Store cookies in an airtight container at room temperature for up to 3 days or in the refrigerator for up to 1 week.