Make the cake:

1. Stir the oil and sugars together. Add the eggs and vanilla and stir to combine.
2. Add the dry ingredients: flour, baking soda, salt and cinnamon. Stir as few times as possible, just until you can’t see the flour in the batter anymore.
3. Add carrot and nuts if you're using them, and fold into the batter with no more than 5 strokes of your spatula.
4. Divide the batter between two greased 8 inch pans or three greased 6 inch pans.
5. Bake at 325F or 160C for 30 minutes, until the cakes spring back slowly when you poke them or a toothpick poked into the middle of a cupcake comes out clean. Let the cakes sit in their pans for 5 minutes before turning out onto a wire rack to cool.

Make the cream cheese frosting:

1. Take butter and cream cheese out of the fridge a few hours before using to allow them to soften.
2. Using a mixer on the lowest speed, mix the butter and powdered sugar until smooth.
3. Mix in vanilla and salt.
4. Add cream cheese and fold in using a spatula.

Put it all together:

1. Spread some frosting onto the middle of a cake board or plate and press your first layer of cake down onto it, to attach it.
2. Spread frosting to cover the top of the cake layer, as filling. Lower your next cake layer on top. If you're making a three layer cake, repeat with another layer of filling and the final cake layer.
3. Put the cake into the fridge for 30 minutes or the freezer for 15 minutes to chill. Then spread cream cheese frosting over the top and sides of the cake. Smooth with a cake scraper or add texture by dragging an offset spatula (palette knife) or the back of a spoon around the cake.
4. Store this cake in the fridge for up to 3 days but serve at room temperature by taking it out of the fridge 2-4 hours before slicing.