Add the broth, garlic, rosemary, and black pepper to a small saucepan. Bring to a simmer and then remove the garlic and rosemary.
Carefully transfer the hot broth to a blender along with the butter. Hold a kitchen towel over the steam escape in the top of the blender, and blend until foamy. Serve immediately.
This nutritional information refers to each serving of the entire recipe and not just the products used as ingredients.