In a large bowl, whisk together the all-purpose flour, granulated sugar, brown sugar, baking powder, baking soda, ground cinnamon, ground nutmeg, and salt until evenly combined.

Combine wet ingredients

In a separate medium bowl, whisk the eggs until blended. Add the vegetable oil and vanilla extract and whisk until smooth.

Incorporate wet into dry

Make a well in the center of the dry ingredients and pour in the wet mixture. Stir gently with a spatula or wooden spoon until just combined — do not overmix.

Fold in carrots and mix-ins

Fold in the grated carrots, then gently fold in the chopped nuts and raisins if using. Scrape the batter into the prepared pans and smooth the tops evenly.

Bake

Bake on the center rack for 25–35 minutes, until a toothpick inserted into the center comes out with a few moist crumbs (not wet batter) and the cakes are golden and spring back slightly to the touch.

Cool

Remove cakes from oven and let cool in pans on a wire rack for 10 minutes. Run a knife around edges, invert onto racks, remove parchment, and let cool completely (about 1–1.5 hours) before frosting.

Cream Cheese Frosting

Soften and beat

Place the softened cream cheese and softened butter in a large bowl. Using a hand mixer or stand mixer fitted with a paddle, beat on medium speed until smooth and homogenous, about 2 minutes.

Add flavor and sugar

Scrape down the bowl, add the vanilla extract, lemon zest (if using), and salt. Gradually add the powdered sugar, 1 cup at a time, beating on low speed after each addition to incorporate and prevent a powdered sugar cloud. After all sugar is added, increase speed to medium and beat until light and fluffy, about 1–2 minutes. Taste and adjust sweetness or salt as needed.

Chill if needed

If the frosting seems too soft for spreading, chill it in the refrigerator for 15–20 minutes to firm slightly, then re-whip briefly before using.

Assembly / Garnish

Level and layer

If cake layers have domes, level them with a serrated knife or cake leveler. Place the first layer on your serving plate or cake board and spread about one-third to one-half of the frosting evenly over the top (depending on how thick you want the layers).

Top layer and crumb coat

Set the second cake layer on top. Apply a thin crumb coat of frosting over the entire cake (a light layer that traps crumbs). Chill for 15–20 minutes to set the crumb coat.

Final frost

Apply the remaining frosting evenly over the top and sides, using an offset spatula for a smooth finish or a spatula for a rustic look.

Garnish

Sprinkle the toasted chopped nuts around the edge or in the center and add the extra grated carrot for a fresh look. Refrigerate for 30 minutes to set the frosting, then bring to room temperature 30 minutes before serving for best texture.