Prep the pans: Heat oven to 350°F (175°C).
Grease and line two 8-inch round cake pans with parchment. Lightly flour with your GF blend and tap out excess.
Mix dry ingredients: In a large bowl, whisk the gluten-free flour, almond flour, sugars, baking soda, baking powder, salt, cinnamon, and nutmeg until well combined.
Whisk wet ingredients: In a medium bowl, whisk eggs, oil, applesauce, and vanilla until smooth and slightly frothy.
Combine: Pour wet into dry. Stir with a spatula until just combined and no dry pockets remain.
Fold in grated carrots and, if using, nuts and raisins. The batter will be thick.
Bake: Divide evenly between pans. Smooth tops.
Bake 22–28 minutes, until the centers spring back and a toothpick comes out with a few moist crumbs.
Cool: Let cakes cool in pans 10 minutes. Turn out onto a rack, peel parchment, and cool completely. Don’t frost warm cakes.
Make frosting: Beat butter 30 seconds until creamy.
Add cold cream cheese and beat until just smooth. Mix in vanilla and salt. Add powdered sugar in 2–3 additions on low, then beat on medium until fluffy, about 1 minute.
Don’t overbeat.
Assemble: Place one layer on a stand. Spread about 3/4 cup frosting on top. Add second layer and frost the top and sides.
For a rustic look, do a light crumb coat, chill 15 minutes, then finish with a thicker layer.
Finish: Garnish with extra chopped nuts or a light sprinkle of cinnamon, if you like. Slice with a warm knife for clean cuts.