Preheat the oven to 350°F (180°C) and spray a 9x9 square baking pan with non-stick spray. Set aside.
Sift all purpose flour into a mixing bowl and add sugar, baking soda, salt, cinnamon and nutmeg. Mix together.
Add grated carrots, crushed pineapple, oil, vanilla and vinegar and mix into a thick batter. If it seems like it doesn't want to form into a batter, leave the bowl for a couple of minutes and then come back to it. The carrots will release more moisture into the bowl and it will come together into a thick batter.
Add chopped walnuts and mix in.
Transfer the batter to the prepared 9x9 square baking dish and smooth down.
Bake at 350°F for 35 minutes or until a toothpick inserted into the center of the cake comes out clean.
Allow to cool completely before frosting with cream cheese frosting and decorating with chopped walnuts.
Cut into slices and serve.