Serve with Le Cirque chef Craig Hopson's Braised Short Ribs.
Heat butter in a large skillet over medium heat. Add onion and garlic and cook, stirring, until soft and translucent, about 5 minutes. Add kale and season with salt; cook, stirring, until soft, about 10 minutes. Add chicken broth and cover; reduce heat to low and cook until tender and dark green, about 25 minutes. Serve immediately.