In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar together on medium speed until fluffy, about one minute. Add in the egg and vanilla and beat again to incorporate. Next, add the orange zest and ginger and mix again to incorporate. After that, pour in the flour and salt and mix again until just combined. Pat the dough into a flat disc and wrap in plastic wrap. Chill for at least two hours, or until firm.
Preheat oven to 350 F. Flour your work surface and rolling pin and roll dough out into ¼ inch thickness. Then, cut out circles using a glass or 2 inch biscuit cutter. Re-roll scraps and repeat until all the dough is gone. Keep half the circles as the bottoms and for the other half, use a paring knife to cut out various moon phase shapes, being sure to leave about a ¼ inch border around all sides.
Next, working in batches, place all cookies on parchment-lined cookie sheets about an inch apart. Freeze for about 20 minutes, or until frozen solid. Bake for about 8-10 minutes, until lightly brown. Transfer to a wire rack and cool completely.
When all the cookies have baked, make the ganache. Add a large heat-proof bowl over a small pot filled with a few inches of water set over medium heat. Add the chopped chocolate, cream, and salt to the bowl and stir occasionally until melted, being sure to keep the water just barely simmering, but not boiling. Remove from heat and allow to cool and thicken for about 10-15 minutes.
Using an offset spatula, spread about a teaspoon of ganache onto the bottom of a cookie and top with a top cookie. Repeat until all cookies are assembled.