Preheat the oven to 375ºF. Bring a large pot of water to a boil. Add 2 tablespoons kosher salt. Boil the pasta for 6 minutes; then drain and rinse under cold water.
Transfer the pasta to a large bowl. Pat dry with a dish towel. Add the tomato sauce, heavy cream, parmesan, and 4 ounces of the mozzarella. Stir to combine.
If you are adding the kale and sausage, place the sausage in a large skillet over high heat. As soon as it begins to sizzle, turn the heat to medium, and use a spoon to break it into smaller pieces. Cook for 5 to 7 minutes, stirring occasionally to ensure it browns evenly. Transfer the sausage to the large bowl, leaving the fat behind. Add 1 tablespoon of extra-virgin olive oil to the skillet and set over medium-high heat. Add the kale and season with a pinch of salt. Cook for 2 to 4 minutes, using tongs to stir and rearrange the kale in the skillet until it is wilted down. Transfer the kale to the bowl and stir to combine.
Transfer everything to a 9×13-inch baking dish (or disposable foil pan if you are gifting to a friend). Top with the remaining 4 ounces of mozzarella.
Transfer to the oven and bake for 35 minutes or until the mixture is bubbly and the edges are browned to your liking. Let cool briefly before serving.
