Turn on the Instant Pot to 'Sauté' and using the 'Adjust' button, adjust the sauté heat level to 'Normal' and allow it to heat up for a few minutes before adding the butter. I usually wait for the display to read 'Hot'.
Add the butter and, using a spoon or spatula, move the butter around the pot as it melts. Once the butter has melted and starts to get hot, add the onion and cook, stirring occasionally until it starts to become soft and translucent, usually 4 to 5 minutes. Do not allow the onions to brown.
Turn off the 'Sauté' function and add the two cans of diced tomatoes with the juices, chicken stock and salt to the pot and give everything a good stir. Next, add the tomato paste to the pot without mixing it in and place the sprig of fresh basil on top of the soup.
Close the pot and set the pressure release valve to 'Sealing', then select the 'Soup' function at 'High Pressure' and adjust the cook time to 10 minutes.
Once the cook time has completed, allow for a 5 minute NPR (natural pressure release). Release any remaining pressure and then open the pot, discard the basil and allow the soup to cool for a few minutes. After the soup has cooled enough to stop bubbling, use an immersion blender to puree the soup until it is smooth.
Add the heavy cream and honey and blend into the soup.