You've never had spice cookies like these. A secret ingredient--black pepper--adds just a hint of heat.
Preheat oven to 375°F with oven racks in top third and bottom third of oven. Beat butter and brown sugar with an electric mixer on medium speed until light and fluffy, about 2 minutes. Add molasses and vanilla, and beat on low speed just until combined. Add egg, and beat on medium speed until mixture thickens slightly, about 30 seconds. Whisk together flour, baking powder, baking soda, salt, cinnamon, ginger, and pepper in a medium bowl. Gradually add to butter mixture, and beat on low speed just until combined after each addition.
Place sanding sugar in a shallow dish or bowl, and drop dough by heaping tablespoonfuls into sugar, rolling to coat. Place half of coated dough balls about 2 inches apart on parchment paper-lined baking sheets.
Bake in preheated oven until cookies are just set, 8 to 9 minutes, switching pans top rack to bottom rack halfway through baking. Cool on pans 5 minutes; remove cookies to wire racks, and cool completely, about 30 minutes. Repeat with remaining cookie dough.