Creating Nigella Carrot Cake is simple when you follow these step-by-step instructions:

1. Preheat the Oven: Begin by preheating your oven to 350°F (175°C). Prepare two 9-inch round cake pans by greasing and lightly flouring them.
2. Mix Dry Ingredients: In a large mixing bowl, sift together the flour, baking powder, baking soda, ground cinnamon, ground nutmeg, and salt.
3. Mix Wet Ingredients: In another bowl, whisk together the vegetable oil, eggs, granulated sugar, and vanilla extract until blended.
4. Combine Vegetables: Add the grated carrots and crushed pineapple to the wet mixture. If using walnuts, fold them in as well.
5. Combine Mixtures: Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined. Be careful not to over-mix.
6. Divide Batter: Pour the batter equally into the prepared cake pans, smoothing out the tops with a spatula.
7. Bake: Place the cakes in the oven and bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
8. Cool the Cakes: Once baked, remove the cakes from the oven and let them cool in their pans for about 30 minutes. Afterward, transfer them to a wire rack to cool completely.
9. Prepare Cream Cheese Frosting: While the cakes are cooling, prepare the frosting by beating the softened cream cheese and butter together until smooth. Gradually add the powdered sugar and continue beating until fluffy. Stir in the vanilla extract and optional lemon zest for added flavor.
10. Assemble the Cake: Once the cakes are fully cooled, place one layer on a serving plate. Spread a generous layer of cream cheese frosting on top. Place the second layer on top and cover the entire cake with the remaining frosting.
11. Decorate: Optionally, you can decorate the top with additional chopped walnuts or grated carrots for a beautiful finish.

Follow these steps, and you will end up with a delightful Nigella Carrot Cake that is sure to impress!