Press the Sauté button on the Instant Pot. When hot, add the oil and butter.
Add the onion. Cook until soft, stirring occasionally, approximately 5 minutes. Try not to let it brown. Add leeks, cook for additional 3-4 minutes until the leeks are soft.
Add garlic and cook for about 30 seconds, until fragrant, stirring frequently.
Sprinkle the flour over the onion-leeks mixture and stir. Cook for a minute to get the raw taste out of the flour.
Stir in the broth. Be sure to dissolve the flour and scrape the bottom of the pot. The Instant Pot senses particles on the bottom and will shut off to prevent burning.
Add the bay leaf, salt, pepper, and the potatoes. Stir.
Put the lid on the pot and set the steam release knob to the Sealing position.
Press the Manual (or Pressure Cook) button, and the + or - button to choose 7 minutes. then forget about it until the timer goes off.
When the cooking cycle has ended, let the pot naturally release pressure for 10 minutes. Then manually release the remaining steam.
10. When the pin in the lid drops, open it and stir the soup. Remove the bay leaf. Then use an immersion blender to puree it. If you don't have an immersion blender, you can use a blender, pureeing the soup in small batches very carefully.
11. Stir in the cream or half and half.
12. Taste and adjust salt, if needed.