Combine the wet ingredients. In a saucepan, melt the butter, bourbon, molasses, salt, and spices over low heat. Transfer to a bowl and let cool. Once the mixture is just barely lukewarm, beat in the egg.
Mix the dry ingredients. In the bowl of the standing mixer, mix the flour, baking powder, and baking soda. Add the wet ingredients to the dry and beat on medium speed until combined, about 2 minutes.
Chill the dough.. Divide the dough in half and place between two pieces of parchment paper - the dough will be wet. Pat into disks, about 1-inch thick. Refrigerate for at least 1 hour. If the dough is not chilled, it will be tough to roll out.
Roll the dough. Preheat the oven to 350°F. Once the dough has chilled, flour a clean work surface and roll thin - about ¼-inch to ⅛-inch in thickness depending on your taste. Thinner dough equals crispier cookies. If the dough starts to stick while rolling, dust with more flour.
Cut the cookies. Cut out your preferred cookie shapes, transfer to a cookie sheet lined with parchment paper and bake 8 minutes for thin cookies and 10 to 12 minutes for thicker cookies. Form the dough scraps back into a dish and roll out again to cut more cookies. Repeat until all the dough is used.
Decorate. Frost the cookies using the bourbon buttercream recipe below or your favorite holiday icing.