Layered Brown Sugar Spelt Carrot Cake (with Lemon Cream Cheese Frosting)

Name: Layered Brown Sugar Spelt Carrot Cake (with Lemon Cream Cheese Frosting)
Cuisine: American
Ingredients: 250ml (1 cup) vegetable oil; 200g (1 cup) brown sugar; 200g (7 oz) grated carrots (see note 1); 4 eggs (medium); 240g (2 cups) white spelt flour (see note 2); 2 tsp baking powder; ½ tsp nutmeg; 1 tsp cinnamon; 200g (3½ oz) cream cheese; juice of half large lemon (around 2 tbsp); 50g (3½ tbsp) butter; 350g (3 cups) icing / powdered sugar (see note 3); lemon zest & lemon slices