Preheat your oven to 350°F (175°C). Grease the mini bundt cake pan with non-stick spray or butter.

In a mixing bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt until well combined.

In another bowl, combine the granulated sugar, brown sugar, vegetable oil, and eggs. Whisk until smooth.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Fold in the grated carrots and walnuts if using.

Spoon the batter into the prepared mini bundt cake pan, filling each cavity about 2/3 full.

Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pan for 10 minutes before transferring them to a wire rack to cool completely. Serve as is or with cream cheese frosting.