Wash the mushrooms by wiping down gently with a damp cloth.
Separate the stems, giving them an additional rinse to remove all dirt. Pat dry.
Dice both onions and mushroom tops. Mince the stems and garlic.
In your Instant Pot, add in the olive oil, onion, mushroom stems, and 1/2 tsp of salt. Press the Sauté button. Stir every 5 minutes until the cycle is over. At this point, you should have lightly caramelized onions and some fond on the bottom of the pot.
Deglaze the pan with your chardonnay. Then add in the mushroom tops, garlic, soy sauce, and vegetable broth. Season with dried thyme, the remaining 1/2 tsp salt, and pepper.
Put the lid on your Instant Pot with the vent closed, and press the Soup button. This should run a cycle for 20 minutes at High Pressure/Normal.
Blend the soup in the Instant Pot using an immersion blender. Leave as many mushroom chunks as you like.
At this stage, you may stir in the heavy cream.
Taste to season, and season to taste (add salt and pepper if you want more). You may also run an additional Sauté cycle for 35 minutes to reduce the liquid for a thicker soup.
Makes 3 2-cup servings. Store leftovers in pint jars in the fridge for up to a week.