Preheat the oven to 160°C and line the baking tin with parchment paper (I used a square 25 x 25 cm baking tin, you can also use two smaller round cake tins not more than 20cm in diameter and divide the cake mix between them).
In a large bowl beat together eggs, sugar and oil until properly incorporated.
Mix grated butternut squash, grated carrot, walnuts, rum and vanilla into the wet ingredients.
In a separate bowl sift together flour, spices, bicarbonate of soda, baking powder and salt. Make sure they are combined evenly.
Gently fold the dry ingredients into the wet mix. Pour the mix to the lined tin and level the surface.
Bake on 160°C for around 40 minutes. (Two round tins might be done sooner so keep checking). The sponge is baked once the testing skewer comes out clean.
Remove the sponge from the tin and let the cake cool down completely.
HOW TO MAKE THE CREAM CHEESE FROSTING
Sift icing sugar into the bowl. Sifting helps to break unwanted lumps in the sugar for the very smooth frosting.
Add the butter and whisk until combined and smooth.
Add cream cheese into the butter spoon at the time (If your butter and cream cheese don’t have the same temperature the mix will more likely curdle).
FINISHING THE CAKE
If you baked the cake in a single tin, cut it in half to create two identically shaped sponges.
Use a little bit less than half of the frosting and spread it onto one of the cake layers. Sandwich the other layer on top of it.
Thinly cover the sides of the cake with the frosting and spread the rest evenly over the top.
Optional: Decorate the sides of the cake with chopped walnuts.
Let the cake chill in the fridge for at least an hour before serving.