Remove the ends and peel the pumpkin, then cut it in half and scoop out the seeds and pulp. Dice the onion.

Cut the pumpkin into small pieces and steam them in a rice cooker until tender.

Heat a soup pot and add the unsalted butter and diced onion. Sauté briefly, then add the pumpkin and stir-fry. Pour in the milk and bring to a simmer over low heat.

Turn off the heat, then use a food processor to puree the pumpkin in the pot.