Melt the butter in a large, heavy based stockpot over medium heat. Add the leek and cook until softened (approximately 2-3 minutes). Add the pumpkin, rosemary and thyme. Cook, stirring, for 2 minutes. Pour in the stock and bring to the boil.
Reduce the heat to low, then simmer, stirring regularly to ensure there is enough moisture. Cook until pumpkin is just tender (approximately 20-30 minutes depending on the size of the pumpkin pieces). Add extra stock, if required.
Allow to cool slightly, then blend in batches. Return soup to stockpot and reheat gently.
Serve with pane di casa or ciabatta bread – buon appetito.