1. The pumpkin
Place the pumpkin cubes in a saucepan. Cover with water and bring to the boil. Leave to cook for about fifteen minutes, then drain.
Using a potato masher, mash the pumpkin pieces and add the butter. Mix well, season and set aside.
2. The rice
Put the olive oil in a frying pan and bring to a low heat.
Add the chopped onion and sweat for five minutes.
Add the garlic and the arborio rice.
Stir until the mixture coats the rice grains well and they become translucent.
Add the dry white wine and stir until it has evaporated.
Add the vegetable stock ladle by ladle until it is absorbed in between. Stir regularly and repeat the operation until there is no stock left.
3. Assembly
Add the pumpkin purée, mascarpone and sage.
Mix well, then add the nuts. Check the seasoning and serve.