Spice Roll-Out Cookies

Sift flour, ginger, cinnamon, baking soda, salt, allspice, nutmeg, mustard, and cloves into large bowl. Using electric mixer, beat butter in another large bowl at medium speed until smooth and creamy, about 2 minutes. Add brown sugar; beat 1 minute. Add molasses; beat until fluffy, about 2 minutes. Add egg; beat until well blended, about 1 minute. Reduce speed to low; beat in vanilla. Add flour mixture; beat on low speed just to blend. Gather dough into ball; divide in half. Form each half into ball; flatten into disk. Wrap disks separately in plastic; chill until firm, at least 4 hours. DO AHEAD: Can be made 2 days ahead. Keep chilled. Position rack in center of oven; preheat to 350 °F. Line 2 baking sheets with parchment paper. Working with 1 disk at a time, roll out dough between 2 sheets of waxed paper to 1/8-inch thickness for smaller (2-inch) cookies and 1/4-inch thickness for larger (3- to 4-inch) cookies. Using decorative cookie cutters, cut out cookies and transfer to prepared sheets, spacing 1 inch apart. If cookies become too soft to transfer to baking sheets, place in freezer on waxed paper for 5 minutes before continuing. Gather scraps, roll out dough, and cut more cookies, repeating until all dough is used. If not icing cookies, decorate with sprinkles or other sugar toppings, if desired. Bake 1 sheet at a time until cookies are firm on top and slightly darker around edges, about 8 minutes for smaller cookies and up to 12 minutes for larger cookies. Cool completely on rack. Line baking sheets with fresh parchment as needed. Decorate cookies with Royal Icing, then sprinkles or other sugar toppings, if desired. Let stand until icing sets. DO AHEAD: Cookies can be made 4 days ahead. Store between sheets of waxed paper in airtight containers at room temperature.