Heat the Instant Pot on Sauté. Add the butter and melt. Add the onions and cook for 5 minutes, or until the onions are softened and beginning to brown.
Pour in the tomatoes, sugar, chicken broth, and basil over the onions. Stir to combine. Cover the Instant Pot and cook on high pressure for 7 minutes.
Quick release or naturally release the pressure. (I’ve done both, depending on how much of a hurry I was in. It won’t affect the end result). Carefully transfer the hot mixture to a blender, and blend until smooth. Return the soup to the Instant Pot.
Stir in the heavy cream. Serve immediately with grated Parmesan, croutons, or bread (optional).
