For the cookies: Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment, beat the sugar and butter together until fluffy. Add the eggs, one at a time, until the mixture is smooth. Scrape down the sides of the bowl, and mix in the orange zest. Sift the flour, baking powder and salt together, and add to the butter mixture, mixing until just combined. Wrap the dough in plastic wrap, and refrigerate for 30 minutes.
Roll the dough to 1/4-inch thick and cut out cookies with a cookie cutter (about 20 large cookies). Place the cookies on the prepared baking sheet, and sprinkle the tops with sugar. Bake just until the edges start to brown, 8 to 14 minutes, depending on the size of the cookies. Cool the cookies completely.
For the ganache: Place the chocolate in a medium bowl. Bring the heavy cream to a boil and pour over the chocolate to melt. Stir until shiny and smooth, then add rum to taste. Mix until incorporated, and then rest the ganache until firm. Transfer to a piping bag and pipe the ganache onto half of the cookies. Press the second half of the cookies onto the ganache-covered cookies to make cookie sandwiches.
Add as little or as much rum as you like; the recipe is also great without any rum.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.