Turn the Instant Pot on to the sauté function and allow it to heat up.
Add the vegan butter and wait until it is melted.
Once melted, add the diced onion, carrot, and celery. Stir to combine.
Once the onion is almost translucent, add the minced garlic and sauté.
Add the potatoes, then the vegetable broth and stir to combine.
Turn off the sauté function.
Close the lid, set the valve to sealing, and pressure cook on HIGH for 8 minutes. It will take 3-5 minutes for the pot to come to pressure.
Once the 8 minutes are up, press CANCEL and let the pot sit undisturbed for 10 minutes (also known as Natural Pressure Release).
While the Instant Pot is pressure cooking, whisk together the almond milk and flour in a separate bowl or measuring cup. Mix until there are no remaining clumps.
After the 10 minute natural pressure release, turn the pressure valve to venting and release any remaining pressure. Remove the lid.
Stir the soup, then set the Instant Pot to sauté once again.
Mix in the frozen peas at this step.
Pour in the milk and flour mixture and immediately stir to combine.
This should significantly thicken the soup, but go ahead and stir in the plant-based heavy cream if you need more creaminess.
Season with salt and pepper, serve hot, and enjoy!