Cook the Rigatoni: Bring a large pot of water to a boil. Add the salt and cook the rigatoni according to the package instructions until al dente. Reserve 1/4 cup of the pasta cooking water before draining.
Sauté the Garlic and Sausage: In a separate large skillet, melt the butter over medium heat. Add the chopped garlic and sauté for about a minute until fragrant. Then add the ground Italian sausage to the skillet and cook until browned, breaking it into small pieces with a spoon.
Add the Eggplant: Add the cubed eggplant to the skillet with the sausage. Sauté for about 5 minutes, stirring occasionally, until the eggplant is tender and slightly golden.
Incorporate the Tomato Paste: Stir in the tomato paste and cook for an additional minute, allowing the flavors to meld together.
Pour in the Cream and Pasta Water: Reduce the heat to low and pour in the heavy cream, parmesan cheese and reserved pasta cooking water. Stir well to combine, creating a creamy and luscious sauce that coats the sausage and eggplant.
Combine the Rigatoni: Add the cooked rigatoni to the skillet and toss gently to coat the pasta with the sauce. Allow the flavors to mingle for a couple of minutes over low heat.
Season and Serve: Season with black pepper to taste.
Plate and Enjoy: Transfer the Rigatoni with Eggplant and Sausage to individual serving plates or a large platter. Garnish with freshly ground black pepper and basil if desired.