Trim the ribs of any excess fat.
Using the pressure cooker as a saucepan, heat it up, add the olive oil and a pinch of ground black pepper.
Brown the ribs for 5 minutes, turning them often.
Remove the ribs and set to one side.
Add the butter, yes, I know! It is a treat. Sauté the butter for a minute or so, don't allow it to burn.
Add the stock, the ribs and the remaining ingredients and stir well.
Place the lid on the pressure cooker, bring to 15 psi or high and cook for 2 hours.
Allow the pressure to reduce by the natural release method.
Separate the meat from the bones and add back to the gravy.
Remove and discard any bones, the rosemary sprig and the bay leaf.
Carefully check for any softer bones that may have disintegrated during the cooking process.
Allow to cool completely and skim and discard any fat. There was no surface fat when I cooked this though.
Add to a food processor and blend to a rough puree.
Store in the fridge or freeze in batches for later use.