How to Make It
In a small saucepan, bring the cream to a boil. Simmer over moderately low heat, stirring often, until reduced to 1/3 cup, about 7 minutes.
Meanwhile, in a large pot of boiling water, cook the kale until tender, about 5 minutes. Drain the kale, and when it's cool enough to handle, gently squeeze out the excess water. Coarsely chop the kale.
In a large, deep skillet, melt the butter in the olive oil. Add the onion and cook over moderately low heat, stirring occasionally, until softened, about 7 minutes. Add the curry powder and cook over moderate heat, stirring, until fragrant, about 3 minutes. Stir in the chicken broth and water chestnuts and bring to a boil. Add the kale and reduced cream and toss. Cover and cook over moderate heat, stirring a few times, until the kale is sizzling, about 3 minutes. Season with salt and pepper and serve.