Heat the butter and oil in a heavy bottomed stockpot, add the onions, and cook over medium low heat for 10 minutes, or until translucent.
Add the pumpkin puree, butternut squash, vegetable broth, salt, and pepper. Cover and simmer over medium – low heat for about 20 minutes, until the butternut squash is very tender.
Process the mixture through the medium blade of a food mill. Return to the pot, add the heavy cream, and heat slowly. If the soup needs more flavor, add another teaspoon of salt. Serve with croutons.
How to Make the Pesto Croutons
Combine all the ingredients except for the bread cubes in a tall container. Take a an immersion blender and pulse everything together until the mixture looks like a paste. If mixture is too thick, add more olive oil. Combine the pesto and bread cubes in a large mixing bowl and toss everything together until the bread cubes are fully coated.
Cook the coated bread cubes in 2-3 batches over medium heat in a non stick pan until bread is fully toasted and crunchy. Careful not to burn. Serve over soups or salads.