Prepare the Cake Pans: Preheat the oven to 350°F. Lightly grease two 9-inch round cake pans with baking spray or butter, then line the bottoms with parchment paper.
Combine Dry Ingredients: In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, ground cinnamon, and ground nutmeg until evenly combined.
Mix Wet Ingredients: In a separate medium bowl, whisk together the vegetable oil, packed light brown sugar, granulated sugar, room-temperature eggs, and vanilla extract until the mixture is well combined.
Make the Batter: Pour the wet mixture into the bowl of dry ingredients. Stir just until the ingredients are combined and only a few streaks of flour remain. Avoid unnecessarily mixing the batter.
Add Carrots Pecans: Fold the grated carrots and chopped pecans into the batter until they are evenly distributed.
Fill Cake Pans: Divide the batter evenly between the two prepared 9-inch cake pans.
Bake the Cake: Bake at 350°F for 30 to 35 minutes, or until a toothpick inserted into the center of each cake layer comes out clean.
Cool the Layers: Place the cake pans on a wire cooling rack and allow the layers to cool completely in the pans. Once completely cooled, invert the layers and carefully remove the parchment paper.
Beat the Butter: For the frosting, place the softened butter in a large mixing bowl. Using an electric hand mixer or a stand mixer fitted with the paddle attachment, beat on medium speed until the butter is very soft and smooth, about 1 minute.
Add Cream Cheese: Add the room-temperature cream cheese and beat until the mixture becomes fluffy, about 30 seconds.
Add Powdered Sugar: Reduce the mixer to low speed and gradually add the powdered sugar. Use 4 cups for a softer frosting or up to 5 cups for a firmer, sweeter frosting.
Finish the Frosting: Scrape down the sides of the bowl and add the vanilla extract. Beat on medium-low speed for about 1 minute, until the frosting is fluffy and easily spreadable.
Layer the Cake: Place one completely cooled cake layer top-side up on a cake stand or serving platter. Spread ¾ cup of frosting evenly over the top, taking it all the way to the edge.
Stack the Layers: Place the second cake layer top-side down over the frosted first layer.
Frost the Cake: Spread the remaining cream cheese frosting over the top and sides of the assembled cake until evenly covered.
Decorate the Cake: If desired, reserve some frosting for piping decorations onto the cake, or press chopped toasted pecans onto the frosting.
Chill Before Slicing: Refrigerate the assembled cake for 30 minutes to allow the frosting to set before slicing.
Store Leftovers: Keep any leftover cake covered and refrigerated for up to 1 week.
