1. Preheat oven to 350 degrees.
2. Sift together flour, baking powder, baking soda, cinnamon, salt, nutmeg and allspice in a large bowl.
3. Use an electric mixer to combine brown sugar and oil. Add the eggs and vanilla and beat on high speed for about a minute.
4. Combine the wet mixture with the dry stuff. Mix on low speed until all ingredients are incorporated then crank up the speed and blend on high until batter is smooth.
5. Add shredded carrot, walnuts, and raisins and mix by hand. Pour batter into a 13x9-inch baking pan that has been generously greased with shortening.
6. Bake for 40 to 50 minutes or until a toothpick stuck in the center comes out clean. Allow the cake to cool completely.
7. Make the frosting by mixing softened cream cheese, milk, and vanilla in a large bowl with an electric mixer. Add the powdered sugar, one cup at a time, and blend well until frosting is smooth.
8. When the cake has cooled, frost the top with the entire bowl of cream cheese frosting. Sprinkle the pecans over the frosting. Slice into 12 pieces to serve. Cover the leftover cake and store it in the fridge.