Turn Instant Pot onto saute and add olive oil and onions. Saute until onions are soft and translucent. Add in garlic and stir for another 30 seconds.
Add in remaining ingredients and stir to combine.
Put on the lid, set valve to sealing and set on high pressure for 15 minutes if using fresh tomatoes and set for 8 minutes if using roasted tomatoes. When cycle is done, turn the Instant Pot off so it doesn't enter the warming stage. Allow a natural release for 15-20 minutes.
Remove lid and blend soup to desired consistency using an immersion blender or a high speed blender.
Garnish with some additional fresh basil and freshly grated Parmesan cheese
Tomatoes: You do not have to peel the tomatoes, I love the texture the peels gives the soup but if you prefer, you can definitely peel them.Using roasted tomatoes adds amazing flavor to the soup but it is also delicious with just fresh tomatoes.Cream: If you prefer, you can add some half and half or whipping cream to the soup to make it richer and creamier, I'd start with a 1/2 cup. Add the cream after blending the soup. Do not add it to the Instant Pot.Blend: You can blend the soup two different ways. You can use an immersion blender or put it into your high speed blender. If you are using a regular blender, only do a little soup at a time as the hot soup can cause the lid to blow off the blender. Blend to desired consistency. I like my soup a little thicker, with more texture.