Boil the pumpkin with a small amount of water. Use a blender to puree the pumpkin, adding the boiling water gradually while blending. Be careful not to make it too watery. (You can also steam the pumpkin and then add water, which works just as well.)

On low heat, melt the butter in a pot. Add the onion and sauté until very soft. Then add the pumpkin. Continue cooking and gradually add milk until you reach your desired thickness.

Season with salt and black pepper. Serve in a bowl, drizzling a little milk on top and sprinkling with black pepper for garnish.