Boil your pasta in well salted water, reserving a cup of pasta water before draining. I tend to undercook dried pasta by about 1 minute from the packet instructions so it can finish cooking in the sauce at the end.
While the pasta cooks, heat the olive oil in a large skillet over medium heat. Add the onion and a big pinch of salt and cook for 4-5 minutes until softened.
Add the garlic and cook for 30 seconds until fragrant. Stir in the smoked paprika and tomato paste and cook for 1 minute, stirring constantly.
Drain the peppers really well, giving them a gentle squeeze to get any liquid out. Give them a rough chop.
Transfer the onion mixture to a blender along with the roasted red peppers and ¼ cup of pasta water from the pot. Blend until smooth. Blender tip: If you have a smoothie maker or high-speed blender, use it here. Roasted peppers can be quite fibrous and a powerful blender will give you a much smoother sauce. Pour the sauce back into the skillet and bring to a gentle simmer. Cook for 2-3 minutes, stirring occasionally to evaporate some of the water.
Lower the heat and stir in the cream, bring to a very gentle simmer.
Add the parmesan in two separate lots, stirring and letting the first melt in before adding the next.
Add the drained pasta and lemon juice, tossing well to coat. Add an extra splash of pasta water if needed to loosen the sauce.
Let it gently bubble away for 1-2 minutes until the pasta is really well coated. Season to taste with salt and pepper.
Serve immediately with extra parmesan and fresh basil or Italian parsley if desired.