Peel and cut the pumpkin into cubes. Cut the carrots and celery are into cubes also, and the leeks into circles. Put 4 1/5 cups (1 liter) of water to boil on the stove and dissolve the broth cubes.
Add all the vegetables and boil for about half an hour. Blend everything, put it on the stove once again, add the cream, salt and pepper.
After a minute, remove from the heat, sprinkle it with sunflower seeds and serve.