Preheat the oven to 350°F (177°C) and grease a 9×13-inch pan. I always use this glass pan.

Whisk the flour, baking powder, baking soda, salt, cinnamon, and other spices together in a large bowl. Set aside.

Whisk the oil, brown sugar, granulated sugar, eggs, and vanilla extract together in a medium bowl. Pour the wet ingredients into the dry ingredients and whisk until combined. Fold in the grated carrots, pineapple, and walnuts.

Spread batter into the prepared pan. Bake for 45-55 minutes. Baking times vary, so keep an eye on yours. The cake is done when a toothpick inserted in the center comes out clean. If you find the top or edges of the cake is/are browning too quickly in the oven, loosely cover it with aluminum foil.

Remove the cake from the oven and set on a wire rack. Allow to cool completely. After about 45 minutes, I usually place it in the refrigerator to speed things up.

In a large bowl using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the cream cheese and butter together on high speed until smooth and creamy. Add 3 confectioners’ sugar, vanilla, and salt. Beat on low speed for 30 seconds, then switch to high speed and beat for 2 minutes. If you want the frosting a little thicker, add the extra 1/4 cup of confectioners sugar (I add it). Spread the frosting on the cooled cake. Refrigerate for 30 minutes before serving. This helps sets the frosting and makes cutting easier.

Cover leftover cake tightly and store in the refrigerator for 5 days.