Set pressure cooker to "sear", adjust time to 15 minutes, press "start/stop", and add butter. When melted, add mushrooms, onions, carrots, and celery.
When vegetables are tender and liquid has evaporated, add chicken. Cook until chicken is golden brown. Add garlic and thyme and stir. Cook until fragrant.
Season with salt and pepper. Add flour and stir. Cook for 1 minute.
Pour in chicken stock and milk then add rice.
Close and lock lid. Set pressure cooker to "poultry", adjust time to 12 minutes, and press "start/stop".
When done, quick release and make sure all pressure is released before opening lid.
Carefully open lid. Season to taste with salt and pepper. Serve hot.
TIP
If soup is too thick, add more chicken stock to thin it out.
