Preheat the oven to 180C/350F. Grease two 8-inch cake pans with cooking spray and lightly dust with almond flour.
In a large mixing bowl, combine almond flour, baking powder, baking soda, cinnamon, nutmeg, and salt. Mix well.
In a separate bowl, beat the eggs and keto brown sugar with a hand mixer until smooth and almost doubled in size. Mix in the vanilla extract.
In a third bowl, whisk together the oil, shredded carrots, shredded coconut, shredded apple, and chopped walnuts until combined.
Fold the dry ingredients into the egg mixture until just combined. Add the carrot mixture and stir until fully incorporated.
Divide the batter evenly between the prepared cake pans.
Bake for 30–35 minutes, or until a skewer inserted in the center comes out mostly clean.
Let the cakes cool in the pans for 10 minutes, then carefully transfer to a wire rack to cool completely.
Once cooled, layer and frost the cake with keto frosting. Let it sit for 30 minutes before serving.