This recipe makes about 20-24 cookies.
Preheat your oven to 350F/175C.
Heat the cream over medium flame until it is steaming and just comes to a boil.
Pour over the chocolate in a bowl and whisk until it comes together.
Set aside at room temperature, or if you are pressed for time, in the refrigerator, to firm up.
In an electric mixer, beat the butter until it is soft and looks a bit like mayo.
Add the powdered sugar and the zest and/or extract. Mix to combine, and then add the egg white. (At this point it will look separated).
Mix in the flour starting on low speed and then increasing to medium until it's combined.
Transfer a quarter of the batter to a piping bag with a large star tip and pipe shapes, making sure that they will match up with at least one another form.
Continue until you have piped all the dough. They will spread just a little bit, but not too much.
Bake for 10-12 minutes, until just starting to brown at the edges.
Pipe the chocolate ganache onto one half and sandwich two together. Repeat until all the cookies are paired.
Optional: You can roll the sides of the cookies in sprinkles, coconut, or toasted nuts for extra pizazz!