Cook the sausage, breaking into pieces as it browns, about 5 minutes.
Drain all but 1 tablespoon of grease from the sausage and return sausage to pot.
Add diced onion and cook, stirring regularly, until softened, about 3 minutes.
Stir in garlic and Italian seasoning. Cook for 1 minute stirring the entire time.
Press cancel.
Pour in 1 cup of chicken broth and scrape up any browned bits from the bottom of the pot.
Add remaining chicken broth.
Add pasta. Do not stir in.
Top pasta with marinara sauce, diced tomatoes, and tomato paste. Do not stir.
Close and lock the lid. Make sure that the pressure release valve is set to sealing.
Press manual high pressure for and adjust the cooking time to 3 minutes.
When the cooking time has ended, do a controlled quick release.
Give everything a good stir before serving.
Notes
Ground Italian sausage: Either hot or mild will work, so choose the level of heat that you prefer.
Chicken stock: You can also use chicken broth. Feel free to use reduced-sodium chicken broth if you prefer.
Mafalda pasta: Mafalda pasta may also be called mini lasagna noodles. If you substitute another type of pasta, you may need to adjust the cooking time.
Marinara sauce: Choose a marinara sauce that has plenty of flavor. Rao's is a great choice.
Salt and ground black pepper: I like to season after cooking because you'll get a truer sense of the flavors at that point.