Cut the kabocha into 2-inch (5 cm) cubes, and steam until soft. Let cool for 10 minutes. Scoop out the flesh and discard the skin.
Put the kabocha flesh in a large saucepan with the salt and sugar. Mash and cook over medium heat until the consistency is similar to mashed potatoes. Add the butter and cream, and cook for another couple minutes. Top with the pumpk