The roasting of the pumpkin seeds is best done with seeds specially harvested to use in bread and soups. These dry seeds are briefly mixed with a sweet liquor (e.g. maple syrup or a honey/water mixture) and then roasted.
For the roasting of the pumpkin the pumpkin is peeled and the seeds removed and discarded. The slice in inch sized parts. Onions are also cut up in 1/2-1 inch size parts. Roast them on an oven tray with a large surface for exposure (single layer) sprinkled with olive oil.
You can compromise to use vegetable broth cubes to make the broth. But better take the extra time to make a good vegetable broth from fresh vegetables. It is rewarding! Or use a previously frozen vegetable broth.
The creamy soup, can handle cream to make it even softer, but often I use just a splash of milk just before serving. The creaminess of the soup allows for it. This will also allow for using oat- or soy- milk to be used, such as to keep dairy out of the dish.
You will surprise your guests with the rather fail safe recipe with a deep taste.