Prepare tortellini according to package directions. Meanwhile, in a large cast-iron or other heavy skillet, cook sausage over medium heat until no longer pink, 6-8 minutes, breaking into crumbles; drain. Stir in pasta sauce; heat through., Drain tortellini, reserving 1 cup cooking water. Add tortellini to sauce and enough reserved cooking water to reach desired consistency; toss to coat. Stir in Parmesan cheese; dollop with mascarpone cheese. If desired, sprinkle with red pepper flakes.