In a medium bowl, whisk together flour, spices, baking soda and salt; set aside.
With an electric mixer, beat butter and brown sugar until light and fluffy. Beat in molasses and egg. With mixer on low, add dry ingredients; mix just until a dough forms.
Divide dough in half; place each half on a piece of lightly floured plastic wrap; pat each half into a 4-inch square. Wrap well; chill until firm, 1 to 2 hours.
Preheat the oven to 350°F.
Working with one half at a time (keeping the other half wrapped and refrigerated), place dough on lightly floured parchment or waxed paper; roll out ¼ inch thick, turning, lifting, and lightly flouring dough (and rolling pin) as necessary. Using paper, lift dough onto a baking sheet; freeze (on paper) until firm, about 20 minutes.
Remove dough from baking sheet. Using a long offset spatula, loosen dough from paper. Cut out shapes, and transfer to baking sheets. Brush off any excess flour. Decorate with sugar or sprinkles, as desired.
Bake, rotating sheets halfway through, until firm and edges just begin to darken, 10-18 minutes (depending on size of cookies). Cool completely on sheets.
Notes
Can store in an airtight container at room temperature for up to a week.