Boil the pasta: Bring a large pot of salted water to a rolling boil. Cook the spaghetti until just shy of al dente.
Reserve about 1 cup of pasta water, then drain.
Sauté the aromatics: In a wide skillet, warm olive oil over medium heat. Add butter. Once melted, add the garlic and a pinch of red pepper flakes.
Cook 30–60 seconds until fragrant, not browned.
Build tomato flavor: Stir in the tomato paste and cook for 1–2 minutes to caramelize it slightly. This deepens the flavor and cuts raw acidity.
Add tomatoes: Pour in the crushed tomatoes. Season with salt and pepper.
Simmer gently for 8–10 minutes, stirring occasionally. If the sauce tastes sharp, add a small pinch of sugar.
Stir in the cream: Lower the heat and add the heavy cream. Start with 3/4 cup, then add more if you want it creamier.
Simmer 2–3 minutes until the color turns rosy and the sauce thickens slightly.
Add cheese and basil: Stir in grated Parmesan and most of the basil. The cheese will melt and help the sauce emulsify.
Toss the pasta: Add the cooked spaghetti to the skillet. Splash in a little reserved pasta water and toss vigorously until the sauce clings to the pasta and turns glossy.
Adjust with more water as needed.
Taste and finish: Season with more salt and pepper if needed. Top with extra basil and Parmesan. Serve hot.