Using both fresh and dried ginger ensures that these cookies have a snappy flavor. For even more spicy-sweet goodness, use up to 1/3 cup fresh ginger.
Whisk together flour, ground ginger, baking soda, and salt. In a large bowl, using a mixer, beat butter and granulated sugar on medium-high until pale and fluffy, 3 minutes, scraping down bowl as needed. Beat in fresh ginger, egg, and molasses. Beat in flour mixture; fold in raisins. Scoop dough into 1 1/2-inch balls onto a parchment-lined baking sheet. Refrigerate until firm, 30 minutes.
Preheat oven 350 degrees, with racks in upper and lower thirds. Roll balls in sanding sugar; place, 2 inches apart, on two parchment-lined baking sheets. Bake until centers are just set, 16 minutes, rotating halfway through. Let cool on sheets on wire racks 5 minutes. Transfer cookies to racks; let cool completely.
Store in an airtight container, up to 1 week.