Clean and slice leeks into half-moon shapes. Cut off the dark green part, trimming to the part where the color is a pale green. Rinse well to get the dirt out of the layers.

Press the Sauté button on the Instant Pot. When the display reads 'Hot', add the oil and butter.

Add the leeks and stir. Cook until soft, stirring occasionally. It's fine if they brown a little.

Add garlic and cook for about 30 seconds, until fragrant, stirring frequently.

Sprinkle the flour over the leeks 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 so you don't get a "burn" issue.

Add the bay leaf, salt, pepper, and the potatoes, nutmeg. 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 +/- button to select 7 minutes.

When the cooking cycle has ended, let the pot sit undisturbed to naturally release the pressure for 15 minutes. Then manually release the remaining steam.

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.

Stir in the half and half.

Taste and adjust salt, if needed.

Garnish with chopped chives and sour cream.

Serve hot or chilled.