Press the Sauté button on the Instant Pot. When the display reads 'Hot', add the olive oil and the butter.
When the butter is melted, add the leeks and cook until softened, stirring occasionally.
Add garlic and cook, stirring frequently, for about 30 seconds until fragrant.
Add the stock and stir. Scrape down the bottom of the Instant Pot to remove any cooked on 'goodness' (this will also prevent a 'burn' error when pressure cooking).
Add the bay leaf, salt, pepper, and the potatoes.
Press cancel to end the saute program, then lock the lid into position on the pot and set the steam release valve to 'Sealing'.
Select 'Pressure Cook' (or 'Manual'), and set it to cook for 7 minutes.
When the pressure cooking time is up, allow it to naturally release the pressure for 10 minutes. Then manually release the remaining steam.
Carefully open the Instant Pot, stir the soup and remove the bay leaf.
Use a stick blender to puree the soup to your desired texture.
Stir through the sour cream, and season with salt and pepper to taste.