Pour about 6 1/5 cups (1.5 L) of water in a pot. Put it on the stove to come to a boil. Peel and cut the pumpkin, potatoes, carrot and leeks into coarse pieces.
Pour them into the boiling water. Add salt and boil until the vegetables soften. Once the vegetables soften, mash them to a smooth mixture.
Add black pepper, a pinch of nutmeg and more salt (if needed).
Serve the soup hot, garnished with cream and seeds.