Preheat the broiler and put a rack in the middle of the oven.

Put the potatoes and the parsnips in a medium pot and cover with water. Bring to a boil, over high heat, then salt the water and cook until the potatoes and parsnips are tender, 15 minutes or so. Drain and return the potatoes and parsnips to the hot pot. Add the horseradish, milk, chives, salt and pepper, to taste, and mash to desired consistency. Stir in 1 cup of the cheese and the egg.

Meanwhile, soak the dried porcini in 2 cups boiling water. Once softened, strain the broth through a paper towel and reserve. Rinse the mushrooms and chop them into small pieces.

Heat a Dutch oven or large skillet over high heat with extra-virgin olive oil or the herb olive oil.  Add the mushrooms, and the rosemary leaves if not using an herbed olive oil, and cook for 10 minutes. Stir in the carrot and onion and season liberally with salt and pepper, to taste. Cook for 5 minutes more, then stir in the garlic and the kale and season with nutmeg. Cook until the kale wilts, about 2 minutes. Stir in the Worcestershire sauce and the stock and mushroom broth (should have 3 cups of broth in total), and bring to a boil. In a small skillet, over low heat, melt the butter, whisk in the flour and cook for 1 minute, then stir it into the sauce and thicken  by boiling for a few minutes. If using a Dutch oven, just top the vegetable mixture with the potato puree. If not, transfer the vegetable mixture to a large casserole and top with the mashed potatoes. Sprinkle with the remaining cheese, and brown under the broiler for 2 to 3 minutes.  Remove from the oven and serve. (If you make it ahead, then reheat the casserole in a 400 degree oven before broiling the cheese)