Set your Instant Pot to Saute mode and let it heat up for about 2 minutes. Add the olive oil, then add the quartered onion. Cook for 3 to 4 minutes, stirring occasionally, until the edges start to soften and turn translucent.

Add the smashed garlic cloves and red pepper flakes. Stir and cook for another 60 seconds until you can smell the garlic. It should be fragrant but not brown.

Press Cancel to turn off Saute mode. Pour in both cans of tomatoes with all their juices, then add the vegetable broth, salt, and black pepper. Give everything a quick stir to combine.

Lock the lid in place and set the valve to Sealing. Pressure cook on High for 10 minutes. When the timer goes off, carefully turn the valve to Venting for a quick release. Wait for all the steam to escape before opening the lid.

Tilt your immersion blender slightly to the side and submerge the head fully before turning it on. Blend the soup directly in the pot until completely smooth, working slowly to avoid any hot splashing. This takes about 60 to 90 seconds.

Stir in the heavy cream and the fresh basil leaves. Let the soup sit on the Keep Warm setting for 2 to 3 minutes so the basil softens slightly and the cream warms through. Taste and adjust salt as needed before serving.