Using a sturdy knife, cut the pumpkin or butternut squash into roughly 1.5” cubes.
Do the same with the potatoes. In a medium saucepan, combine the pumpkin, potatoes, the 3 tablespoons of olive oil, and the water.
Cover and cook over medium-low heat, stirring occasionally, until tender—50 to 60 minutes.
Transfer to a blender jar and purée until smooth (don’t fill the blender more than half full—work in batches if necessary). Salt to taste.
Divide the soup between warmed soup bowls.
Drizzle generously with additional olive oil, and garnish with croutons.