Melt butter in Instant Pot. SAUTE onions, celery, and carrots until tender. Add garlic and cook 1 minute, stirring often. Add chicken stock, tomatoes, basil, tomato paste, salt, and pepper.
Select HIGH PRESSURE and 5 minutes cook time. When beep sounds turn Instant Pot off, wait 5 minutes and then use a quick pressure release to release pressure.
When valve drops, carefully remove lid. Purée mixture until it’s very smooth. You can also use an immersion blender and purée it in the Instant Pot pot.
Select SAUTE and stir in coconut milk. Bring to a simmer and turn off Instant Pot. Serve.