Turn the pressure cooker on and press the Sauté button. Add the olive oil and butter once the screen says "hot".
Add the onion, potatoes, celery, bay leaves, and thyme and stir occasionally until the onions are slightly translucent.
Stir in the carrots, garlic, ham and pepper. Cook for about a minute.
Add 5 cups of broth and bring to a simmer (You'll add the extra broth later if you like a thinner consistency).
Stir in the rinsed split pea.
Put the lid on the pot and lock. Make sure the steam release valve is in the sealed position.
Press the cancel button. Press the Pressure Cook button and set to 20 minutes, high pressure.
After cooking, let the soup NPR for 10 minutes before releasing the steam valve and removing the lid.
Discard the bay leaves and any ham bones if you used them.
Coarsely mash soup to desired consistency. Add up to two cups of chicken broth to thin.
When cooled slightly, taste and add salt as needed.
Transfer to soup bowls, top with sour cream (optional) and enjoy immediately.