Transform Three-Cheese Macaroni into a sophisticated pasta dish, with the addition of sweet Italian sausages and baby spinach.
In a large nonstick skillet, heat olive oil over medium. Add red onion and cook, stirring occasionally, until softened, about 8 minutes. Add sausages and red-pepper flakes and cook, breaking up meat with a wooden spoon, until browned and cooked through, 8 minutes. Add reserved macaroni and cheese to skillet, gently stirring to combine. Stir in heavy cream and spinach, and cook until spinach begins to wilt, 4 minutes. To serve, sprinkle with Parmesan.