Step 1

Whisk together flour, cinnamon, ginger, salt, baking soda, nutmeg, baking powder, and pepper in a medium bowl.

Step 2

Using an electric mixer on medium speed, beat brown sugar and butter until light and creamy, about 3 minutes. Beat in egg and molasses, scraping down sides of bowl as needed, until incorporated, about 2 minutes. Reduce speed to low and add dry ingredients; beat until just combined. Add raisins and mix just to evenly distribute. Cover and chill at least 30 minutes and up to 12 hours.

Step 3

Place a rack in middle of oven; preheat to 350°. Divide dough in half and transfer to a parchment-lined baking sheet. Using wet hands, shape dough into two 12"-long logs (a plastic bowl scraper is helpful for this) and arrange on opposing long sides of baking sheet, spacing 2"–3" from long edges. Lightly flatten top of each log.

Step 4

Bake logs until edges are just set but centers are still soft, 23–26 minutes (logs will spread and crack). Let cool.

Step 5

Whisk powdered sugar and milk in a small bowl until smooth. Glaze should be thick but pourable; thin with more milk if needed. Drizzle glaze erratically over logs; let sit until set, at least 30 minutes. Using a serrated knife, slice logs crosswise 1" thick (or slice 2" thick and cut in half down the center for a squarish cookie).Do ahead Cookies can be assembled 4 days ahead. Store airtight at room temperature.