1. In the bowl of your stand mixer, add the butter and sugar and beat on medium speed until light and fluffy. Add the molasses and egg and mix until combined.
2. Meanwhile, combine the flour, baking soda, cinnamon, nutmeg, ginger and salt in a bowl.
3. Add the dry ingredients to the wet ingredients, mixing until fully combined. Turn out the dough onto a piece of wax paper, wrap up and refrigerate for 30 minutes.
5. Remove from the fridge, roll into a log and refrigerate again until fully chilled, at least a few hours.
6. Preheat the oven to 375 degrees and line large baking sheets with parchment paper.
7. Slice the dough log into ½ inch rounds, then cut into quarters and place 2 inches apart on the prepared baking sheets.
8. Bake for 8-10 minutes or until set. Remove from the oven and cool on cooling racks.
9. Match up like size cookies. Spread buttercream onto the bottom of one cookie and top with the other, creating a sandwich.