Meanwhile, add the olive oil, onion, and garlic to a large pan. Turn on the heat to medium. Sauté the onions and garlic until they are softened, about 5 to 7 minutes.
Add the crushed tomatoes and stir until well combined.
Reduce the heat to medium-low and simmer for 15 minutes.
While the sauce is simmering, boil the pasta according to the package directions. When there is about 1 minute of cook time remaining, scoop out 1/2 cup of the pasta water and set it aside. Drain the pasta.
Turn the heat off the sauce and stir in the basil and salt.
Add the pasta and toss to coat. If the sauce became too thick while simmering, add some of the reserved pasta water. (see note)
Notes
The sauce should be "saucy" but not runny. Add a splash at a time until the sauce is a nice consistency.