Step 1: Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or line bottoms with parchment paper.
Step 2: In a large bowl, whisk together flour, baking soda, salt, cinnamon, and nutmeg.
Step 3: In a separate large bowl, whisk together granulated sugar, brown sugar, eggs, vegetable oil, and vanilla extract until well combined.
Step 4: Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Step 5: Fold in the freshly grated carrots and any optional chopped pecans or raisins.
Step 6: Divide the batter evenly between the prepared cake pans. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Step 7: Let cakes cool in pans for 10 minutes before inverting onto a wire rack to cool completely. Once cooled, cut the cakes into 1-inch cubes.
Step 8: In a large bowl with an electric mixer, beat the softened cream cheese and unsalted butter together on medium speed until smooth and creamy, about 2-3 minutes.
Step 9: Gradually add the sifted powdered sugar, vanilla extract, and salt. Beat on low speed until combined, then increase to medium-high and beat until light and fluffy. Be careful not to overmix. If the frosting is too thin, chill for 15-20 minutes.
Step 10: In a large trifle bowl (or individual glasses), place about one-third of the carrot cake cubes in an even layer at the bottom.
Step 11: Spread about one-third of the cream cheese frosting evenly over the cake layer.
Step 12: Sprinkle with about one-third of the chopped toasted pecans.
Step 13: Repeat the layers two more times, ending with a final layer of frosting on top.
Step 14: Garnish the top with remaining chopped toasted pecans or decorative carrot curls.
Step 15: Cover the trifle with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow flavors to meld and the cake to soften.
Step 16: Serve chilled and enjoy!