In a wide frying pan, melt the butter over medium-high heat. Add the onions and mushrooms and cook, stirring occasionally, until the onions are softened, 4-5 minutes. Add the garlic and cook for 1 minute. Add the kale and cook, stirring occasionally, for 3 minutes, until wilted and not quite tender. Push the vegetables off to one side of the pan and add the shrimp. Cook, stirring occasionally, until almost opaque, about 3 minutes. Add the soy sauce, white wine, and cream, if using, and toss to combine. Cook 2-3 minutes, until the sauce begins to thicken.
Serve hot.