Cook the pasta in salted water according to package directions until al dente. Reserve about 1/2 cup of the pasta water, then drain.
Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the onion and cook until softened, about 4 to 5 minutes.
Add the garlic and cook for 30 seconds, then stir in the roasted red peppers and tomato paste. Cook for 1 to 2 minutes.
Transfer the pepper mixture to a blender with the vegetable broth and blend until smooth.
Return the sauce to the skillet. Stir in the cream, Parmesan, red pepper flakes, salt, and black pepper. Simmer gently for 3 to 4 minutes.
Add the cooked pasta and toss to coat. Use a little reserved pasta water if needed to loosen the sauce.
Serve warm, topped with extra Parmesan if desired.