Place the pumpkin in a saucepan and add enough cold water to almost cover. Add 2 tsp sea salt and simmer gently for 20 minutes, or until the pumpkin is soft. Set aside. Meanwhile, dice 50g butter and place it in a heavy-based saucepan over a low heat.

Add the onion and remaining salt and sauté for about 5 minutes or until the onion is very soft. Add the pumpkin and cook for a further 2 minutes.

Pass the mixture through a mouli or blend it in a food processor or blender. Finely dice the remaining butter and stir it into the purée until melted. Check the seasoning.