Wash kale. Remove and discard stems and tear leaves into large pieces.
High Power Blender Instructions
Heat butter in a large skillet over medium heat. Cook onion until softened. Add garlic and salt and cook, stirring constantly, until garlic is fragrant.
Add kale leaves to the skillet and cook, stirring often, until kale is wilted.
Add all ingredients to blender. Blend on high power until completely smooth and steaming hot, about 5-6 minutes. (Or use the Hot Soup button).
Stovetop Instructions
Heat butter in a medium saucepan over medium heat. Cook onion until softened. Add garlic and salt and cook, stirring constantly, until garlic is fragrant.
Add bone broth to saucepan, increase heat to medium high, and bring to a boil. Add kale, reduce heat to medium, and simmer until kale is tender, about 10 minutes.
Add heavy whipping cream to saucepan. Blend soup with an immersion blender until smooth OR transfer soup to a regular blender, remove center stopper from blender lid to allow steam to escape, cover blender with a towel to prevent splatters, and blend until smooth. Take care not to overfill your blender. Blend soup in batches if necessary.
Notes
Other greens, such as swiss chard or collard greens, can be used in place of the kale.