Chop carrots, celery, and onion. Add oil to Instant Pot or other pressure cooker and choose "sauté." Once the oil is hot, add chopped carrots, celery, and onion, then saute for a couple of minutes.
Add minced garlic and saute for another minute. Wash split peas in a strainer, then add to the Instant Pot, along with thyme, bay leaves, and black pepper. Stir to combine.
Add ham bone and water, then fasten the lid and turn the valve to sealing position. Select high pressure and set the time to 15 minutes.
Once the cooking time is complete, do a natural release for 15 minutes, then a quick release. Remove the ham bone, then use a knife to trim the meat off and chop it into cubes. Stir the cubed ham into the soup and taste, adjusting the seasoning with salt if needed. Stir in milk (or half-and-half or cream) before serving.
Notes
It will take approximately 15 minutes for your pressure cooker to come to pressure.
If you prefer a smooth texture, use an immersion blender to blend the soup until creamy, then add diced ham
Store leftover split pea soup in the refrigerator in an airtight container for up to 5 days.
Leftovers can also be frozen for up to 3 months; however, do so before adding milk or cream to the soup.
To thaw, place the soup in the fridge until thawed, then heat it in the microwave or on the stovetop.