Optional: If the marinara sauce is chunky, blend it smooth. This ensures that the broth is very smooth at the end, but is optional if your family doesn't mind more texture.
Add the olive oil to a medium pot over medium heat. When warm, add the marinara sauce and cook, stirring occasionally for 2 minutes.
Add the broth and raise the heat to high. When the broth starts to boil, turn down the heat to medium so it simmers.
Add the pasta. Cook for about 8 minutes, stirring occasionally.
Stir in the Parmesan.
Season to taste with salt and pepper. Serve warm, adding more broth if desired.
Notes
Store leftovers in an airtight container for up to 5 days in the fridge. Warm in a small pot on the stovetop or in a heat-safe bowl in the microwave, adding more broth if desired.
You can also freeze portions of this soup in a freezer container. Thaw overnight in the fridge and warm in a small pot on the stovetop or in a heat-safe bowl in the microwave.
Use vegetable broth to make this vegetarian.
Simmer a Parmesan rind in the broth for extra flavor.