Method:
Put kale and 1/2 cup vegetable broth in a large pot and place over medium heat. Cook, covered, stirring frequently, until kale is wilted, about 3 minutes. Add squash and continue cooking, stirring occasionally, until kale and squash are tender but not mushy, 10 to 12 minutes. Cool to room temperature.
Meanwhile, combine the remaining 1/2 cup broth, onion, dates and vinegar in a small saucepan. Bring to a boil, lower heat, and simmer, uncovered, until onion is very tender and liquid is reduced by half, about 6 minutes. Cool, toss with kale and butternut and serve room temperature or chilled.