01 -
Preheat oven to 350°F. Grease and flour a 9 x 13-inch baking dish.
02 -
In a medium bowl, whisk together the flour, baking soda, baking powder, salt, cinnamon, and nutmeg.
03 -
In a large bowl, stir together the grated zucchini, eggs, vegetable oil, granulated sugar, brown sugar, and vanilla extract.
04 -
Add the flour mixture to the zucchini mixture in several intervals, mixing just until combined. Fold in the walnuts.
05 -
Pour the batter into the prepared baking dish. Bake for 35–40 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs. Start checking for doneness after 35 minutes and every 3 minutes thereafter. Allow to cool completely.
06 -
Using a stand mixer with a paddle attachment, beat the butter, cream cheese, cinnamon, and vanilla extract until light, fluffy, and smooth. Turn the mixer to low and gradually add the powdered sugar, beating until well combined. Scrape down the bowl and beaters as needed.
07 -
Spread frosting on the fully cooled cake. Refrigerate until ready to serve.