Preheat the oven to 350°F then grease and flour a 9x5-inch loaf pan.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In a large bowl, whisk together the vegetable oil, granulated sugar, brown sugar, eggs, and vanilla extract until smooth. Stir in the grated carrots.
Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Fold in the walnuts then pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for 60 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and let cool in the pan for 10 minutes. Then, transfer to a wire rack to cool completely.
While the cake is cooling, prepare the cream cheese frosting. In a medium bowl, beat the cream cheese and butter until smooth and creamy.
Add the powdered sugar, salt, and vanilla extract, beating until smooth.
Once the cake is completely cool, spread the cream cheese frosting over the top. Decorate with extra walnuts if you'd like.
Slice and serve!
