Preheat the oven to 400°. Wrap the garlic in a foil packet and roast for 50 minutes, until softened. Meanwhile, in a small roasting pan, toss the broccoli with the olive oil and butter and season with salt and pepper. Roast for 20 minutes, or until tender.
Squeeze the garlic cloves from their skins into a blender. Add the roasted broccoli, cream cheese and broth and puree until smooth. Transfer the soup to a saucepan and bring to a simmer. Season with salt and pepper and serve with croutons.