Process the raisins and crystallized ginger in a food processor until the mixture sticks together, about 10 seconds. Transfer the mixture to a large bowl.

Heat the unsalted butter in a small saucepan over medium-low heat, swirling the pan occasionally, until nutty brown in color, about 10 minutes. Stir in the ground cinnamon and ground allspice, cook for an additional 15 seconds, then remove from the heat. Stir the butter mixture into the raisin mixture until well combined; allow to cool completely.

In a small bowl, whisk together the all-purpose flour, baking soda and salt.

Whisk the dark brown sugar, molasses and eggs into the raisin mixture until thoroughly combined. Using a rubber spatula, fold in the flour mixture (the dough will be very sticky). Cover the bowl with plastic wrap and refrigerate for at least 1½ hours, or up to 24 hours.

When ready to bake, adjust the oven racks to the upper-middle and lower-middle positions and preheat the oven to 350 degrees F. Line two baking sheets with parchment paper.

Divide the dough into quarters. Working with one piece of dough at a time, transfer to a lightly floured surface and roll into a 10-inch log. Transfer to a parchment-lined baking sheet and square off the sides. Repeat with the remaining pieces of dough, placing two logs on each baking sheet.

Bake until only a shallow indentation remains on the edges when touched, 15 to 20 minutes, rotating sheets halfway through baking. Allow to cool on the baking sheets for 5 minutes, then transfer the parchment to wire racks to cool completely.

In a small bowl, whisk together the orange juice and powdered sugar until smooth. Drizzle the glaze onto the cooled log and let sit until the glaze hardens, about 15 minutes. Cut logs into 2-inch bars. Cookies can be stored in an airtight container at room temperature for up to 5 days.