Combine the flour, baking soda, salt, and spices in a large bowl; set aside. In the bowl of an electric mixer, beat the butter, brown sugar, and egg on medium until smooth. Add the molasses and beat until fluffy, about 2 minutes. Add the vanilla. Stir in the flour mixture 1 cup at a time, blending until smooth. The dough should gather into a semi-firm mass. (If it's not firm, add another 1/4 to 1/2 cup flour, but not enough to make it crumbly.)
Turn the dough onto a lightly floured surface. Divide in half. Flatten into disks and wrap in plastic. Refrigerate at least 2 hours or up to 1 week.
Preheat oven to 350° F. On a floured surface, roll each disk to 1/8 inch thick. Use gingerbread-man cutters to make shapes. Transfer them to a large, parchment-lined baking sheet, spacing them about 1 inch apart. Decorate, if desired. Bake until firm to the touch, about 12 minutes. Cool slightly before transferring to a rack.