Remove IP lid; press SAUTÉ button. Put butter in the inner pot and cook, stirring often, until butter melts.

Add onion, celery, carrot, garlic and salt; stir to combine. Sauté veggies for 4-5 minutes, stirring often. When done, onion should have softened , but still be translucent in color. Stir in broccoli and vegetable broth, pushing the broccoli down into the broth.

Lock the lid securely on the IP. Flip the pressure release knob to SEALING. Push the CANCEL button to clear the cooking program, then press the MANUAL or PRESSURE COOK button (depending on your machine). Set cooking time for 1 minute at High pressure. Now the machine will start heating up and will take about 8-10 minutes before the Instant Pot reaches full pressure and the 1 minute cooking timer starts.

While soup is coming to pressure/cooking, make the "slurry" which will be used to thicken the soup. Stir half and half, corn starch and hot sauce in a bowl or measuring cup until combined (no lumps). Set aside until soup is done cooking.

Once timed cooking is completed, let the pressure release NATURALLY for 5 minutes (do nothing). After 5 minutes, flip the pressure release knob to VENTING, which allows any remaining steam to release immediately. After all steam has released, carefully remove the lid. Press the CANCEL button, to again reset your Instant Pot, then push the SAUTÉ button again.

Give the "slurry" another quick stir, then add it to the soup. Add cheese, and stir to combine. Continue to stir/simmer soup until cheese melts and soup has slightly thickened. Take a bite, then add more salt or hot sauce, if desired.

Ladle hot soup into serving bowls; garnish with more cheese, if desired. Serve!