Instant Pot Tomato Soup

Turn on a multi-functional pressure cooker (such as Instant Pot) and select Sauté function. Add olive oil, celery, carrot, onion, and garlic. Cook for 5 minutes, stirring occasionally.

Stir in vegetable broth, diced and crushed tomatoes, tomato paste, basil, salt, and pepper. Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 6 minutes. Allow 10 to 15 minutes for pressure to build.

Meanwhile, melt butter in a small saucepan over low heat. Stir in flour until a smooth, thick paste forms, about 3 minutes.

Release pressure naturally for 2 minutes according to manufacturer's instructions. Release remaining pressure by opening the valve to vent.

Use an immersion blender to carefully puree the hot soup. Select Sauté function again; set timer for 3 minutes. Add flour paste, stirring continuously. Add milk, Parmesan cheese, sugar, and red pepper flakes. Season with more salt and pepper if needed. Stir to combine until the timer ends.