Prepare the pumpkin by slicing into 2.25-inch slices, removing the skin and seeds, and then cutting into 1.5-inch chunks.
In a large pot, combine the pumpkin chunks, sliced onion, whole garlic cloves, broth, and water. The liquid should nearly cover the pumpkin. Bring to a boil, then simmer rapidly until the pumpkin is tender, about 10 minutes.
Once the pumpkin is tender, remove the pot from heat. Use an immersion blender to puree the soup until smooth. If using a regular blender, blend in batches and be cautious of the steam.
Season the blended soup with salt and pepper to taste. Gently stir in the cream, but do not boil to prevent the cream from splitting.