Melt the butter in a medium pot, add the onions and scallions, and cook over medium-low heat for 7 minutes, until the onion is soft.
Add the broth, increase the heat to high, and bring to a boil. Add the peas, cumin and cook for 5 minutes.
Season with salt and pepper and add the cilantro. Place the soup in a blender and puree.
Return the soup to the pot, add the cream and serve.