Begin by preheating your oven to 350 degrees Fahrenheit (175 degrees Celsius) and then lightly apply a coat of cooking spray to a sheet cake pan or a 10x15-inch glass casserole dish.
In a bowl, sift together flour, baking powder, cinnamon, baking soda, and salt, making sure all ingredients are well combined.
Using the bowl of a stand mixer, beat eggs until they become foamy. Gradually add in sugar and mix until fully incorporated. Alternating between the flour mixture and oil, begin and end with the flour mixture while beating the batter. Gently fold in the pineapple, carrots, coconut, and walnuts before pouring the batter into the prepared cake pan.
Bake the carrot cake in the oven for about 45 minutes, or until it's fully cooked. Once done, remove it from the oven and allow it to cool for approximately 30 minutes.
To make the frosting, combine softened butter and cream cheese in a bowl, using an electric mixer to whip until it becomes fluffy. Sift powdered sugar and add it to the mixture, along with vanilla extract. Mix until the ingredients are well incorporated and the frosting is fluffy. Spread this delicious frosting over the completely cooled carrot cake.
