Preheat the oven to 375°F. Lightly grease (or line with parchment) a baking sheet., Whisk together the flour, spices, salt and baking soda, and set aside., In a large bowl, beat together the butter and sugar, then beat in the molasses., Add the dry ingredients alternately with the rum., Scoop out round balls of dough about 1 1/2" in diameter; a tablespoon cookie scoop works well here. Place the balls on a baking sheet., Bake the cookies for 11 to 12 minutes, until they crack on top but haven't yet browned around the edges., Remove the cookies from the oven, and let them cool right on the pan.