First, make the pumpkin cream (for the cupcake topping and part of the filling). Peel the skin off the pumpkin, chop it into smaller portions, then boil or microwave it till it's soft (about 5-6 minutes).
Mash the cooked pumpkin then puree it through a sieve.
Process pureed pumpkin, sugar and cream for about a minute then leave the mixture in the fridge while you make the cakes.
In a small bowl of stand mixer, place egg and softened butter (room temperature) and beat until whitish in colour and become creamy.
Add the oil and continue beating.
Sift the flour and baking powder together and add half of it to the stand mixer
Add half the milk and mix.
Add the rest of the flour and milk to combine.
Line the cupcake moulds of the tray with baking paper. Divide the batter evenly into the lined cupcake tray.
Bake in the oven for 25-30 minutes.
Once the cupcakes are done, allow them to cool down completely.
Place the pumpkin cream topping into a piping bag and swirl the mixture on the top of the cakes.
Decorate the Mont Blanc Cakes with pumpkin chips (or anything else you desire).
Notes
I used frozen Japanese pumpkin called "Kabocha" which meat is quite dense like chestnuts. It is necessary to adjust the amount of heavy cream depends on the pumpkin's texture used.