Heat olive oil in a large pot or deep skillet over medium heat. Add onions and cook until translucent, about 3-4 minutes.
Add minced garlic and cook for another 30 seconds until fragrant. Be careful not to burn it!
Pour in the diced tomatoes (with their juice) and add the pasta to the pot. Stir to combine.
Add the broth and bring the mixture to a boil. Reduce heat to medium-low, cover, and simmer for about 10-12 minutes, stirring occasionally to prevent sticking.
Once the pasta is al dente, stir in the heavy cream, Parmesan cheese, and most of the basil (reserve some for garnish). Cook for an additional 2-3 minutes until the sauce thickens.
Season with salt and pepper to taste. If you like it spicy, add a pinch of red pepper flakes.
Remove from heat and let it sit for a few minutes to allow the sauce to thicken further.