1. Cook the Pasta:

1. Bring a large pot of salted water to a boil.
2. Add the pasta and cook according to package directions, or until al dente.
3. Before draining, reserve about 1/2 cup of the starchy pasta water. This will be used to adjust the sauce consistency later.
4. Drain the pasta and set aside.

2. Make the Roasted Red Pepper Puree:

1. Drain the jar of roasted red peppers.
2. In a blender or food processor, combine the drained roasted red peppers and fresh basil leaves.
3. Process until smooth.

3. Sauté the Aromatics:

1. Heat the olive oil in a large skillet or pan over medium heat.
2. Add the diced onion and cook until softened and translucent, about 3-5 minutes.
3. Add the minced garlic and cook for another minute, or until fragrant. Be careful not to burn the garlic.
4. Season with salt and pepper to taste.

4. Build the Sauce:

1. Add the roasted red pepper puree to the skillet with the onions and garlic.
2. Stir to combine.
3. Pour in the heavy cream and stir well.
4. Bring the sauce to a gentle simmer, then reduce the heat to low.

5. Combine Pasta and Sauce:

1. Add the cooked pasta to the skillet with the sauce.
2. Stir to coat the pasta evenly with the sauce.
3. Add the butter and stir until melted and incorporated. This adds richness and helps thicken the sauce.
4. Add pasta water, 1 tablespoon at a time, if needed to thin the sauce to your desired consistency.

6. Serve:

1. Serve immediately.
2. Top with freshly grated Parmesan cheese and chopped fresh parsley.