Preheat oven to 350℉ and line a muffin tin with paper liners (or lightly grease).
In a large bowl, whisk together flour, baking powder, baking soda, cinnamon, allspice, and salt. In another bowl, whisk together brown sugar, oil, eggs, vanilla, and milk until smooth.
Stir in grated carrots, walnuts, and raisins. Pour the wet mixture into the dry ingredients and mix gently until just combined. The batter should be thick but scoopable.
Divide batter evenly among muffin cups, filling each about ¾ full.
Bake for 20-22 minutes, or until a toothpick inserted in the center comes out clean and the tops spring back lightly when touched.
Cool in the pan for 5 minutes, then transfer to a wire rack. Sprinkle with extra chopped walnuts or drizzle with maple syrup once cooled, if desired.