Step 1 Heat the oven to 350 degrees. Line a 9-inch square baking pan with parchment paper and spray with nonstick baking spray.
Step 2 In a large bowl, sift together 2 cups plus 1 tablespoon flour, brown sugar, salt, baking powder, baking soda, cinnamon and allspice.
Step 3Make a well in the center of the dry ingredients and add the vegetable oil and orange juice. Stir quickly to combine and form a batter.
Step 4In a separate bowl, toss the carrots and raisins with the remaining tablespoon flour, then fold in the carrots and raisins with the rest of the batter.
Step 5Pour the batter into the prepared pan and smooth the top. Bake the cake on the center rack of the oven until set and a cake tester comes out clean or until the cake springs back to the touch, 40 to 50 minutes. Do not overbake.
Step 6Remove from the oven and cool the cake on a rack. When the cake is cool, cover with plastic wrap and refrigerate to chill, at least 1 hour and up to 2 days.