To make the cake layers:

1. Using a mixer with a beater/paddle attachment (not a whisk), beat room temperature butter and sugar on medium speed until pale and creamy, about 3 minutes. Scrape down to the bottom of the bowl once during mixing to make sure no butter or sugar is stuck at the bottom.
2. Add room temperature eggs one at a time, mixing on the lowest speed after each addition for 30 seconds. Scrape down to the bottom of the bowl to make sure everything is incorporated before adding the next egg.
3. Add vanilla and mix for about 30 seconds to combine. Add room temperature buttermilk and oil and mix on the lowest speed to incorporate.
4. In a bowl, sift flour, baking soda, baking powder, salt and pumpkin pie spice or cinnamon. Add to the mixing bowl and mix on lowest speed to incorporate, scraping down to the bottom of the mixing bowl to check that batter is evenly mixed.
5. Grease three 8" baking pans with non-stick oil spray or butter. Divide batter equally between the cake pans.
6. Bake at 160ºC or 325ºF for 35 minutes or until the cake bounces back up when you poke it.
7. Leave cakes to cool in their pans for 10 minutes. Use a spatula to loosen the cakes from the edges of the pans and then turn onto a wire cooling rack. Leave to cool completely.
8. Optionally, when the cakes have cooled you can use a serrated knife like a bread knife to trim off any domed tops of the cake layers to leave them level.

To make the buttercream filling and frosting:

1. Take butter and cream cheese out of the fridge 2-4 hours before making this. Sift the sugar to remove any lumps and check that the butter and cream cheese are at room temperature.
2. In a mixer with a beater (paddle) attachment, mix butter and a quarter of the powdered sugar on the lowest speed until incorporated, about one minute.
3. Scrape down to the bottom of the mixing bowl with a spatula to loosen any butter and sugar and add the next quarter of powdered sugar and mix for another minute on low.
4. Scrape down to the bottom of the bowl, add another quarter of the powdered sugar, mix for one minute on low, scrape, and add the final quarter of the powdered sugar and salt. Mix for one more minute on low, adding the vanilla once everything is mixed together and continuing to mix until it's incorporated.
5. Scoop about 1 cup of the buttercream into a small bowl. Add cream cheese and stir until combined. Cover the bowl with cling film or Saran Wrap until you're ready to assemble the cake.
6. Add pumpkin puree and pumpkin pie spice or cinnamon to the rest of the buttercream and stir until combined. Cover and set aside.

To put the pumpkin spice cake together:

1. Spread a bit of cream cheese buttercream onto the middle of a cake board or plate and press your first cake layer down to attach it. Spread cream cheese filling onto the top of the cake and then place another cake layer on top. Repeat with another layer of filling and the final cake layer.
2. Put the cake in the fridge for 30 minutes or the freezer for 15 minutes to chill and set. Then spoon half of the pumpkin buttercream on top and spread with an offset spatula or palette knife to cover the cake. Use a straight edges cake comb or frosting smoother to smooth the frosting but it doesn't need to be perfect yet! Chill in the fridge for another 30 minutes or freezer for 15 minutes to set this crumb coat of frosting.
3. Spoon the rest of the pumpkin buttercream onto the cake and spread to cover the cake. Smooth with a cake comb and optionally, add texture with the back of a spoon.
4. To decorate the cake with pumpkins, add orange food colouring to the leftover pumpkin buttercream and spoon into a piping bag fitted with a small star shaped tip e.g. #32. Starting at the bottom of the cake, pipe two curves for the outer edges of a pumpkin. Pipe curves within those, working towards the middle of the pumpkin. For pumpkins on the top of the cake, pipe a blob of buttercream and then pipe curves to cover that. For stems or stalks, add brown food colouring or melted chocolate to the leftover orange buttercream and spoon into a piping bag fitted with a small round tip e.g #4 or small star tip e.g. #16. Pipe a line on top of each pumpkin.
5. You can refrigerate this cake for 2-3 days but take out 2 hours before serving so that the cake comes to room temperature.