Season short ribs all over with 1 tsp of salt and 1 tsp black pepper. Turn pot to high saute function. Add olive oil. Add ribs and sear for 3 mintues on each side until golden brown. Remove ribs and set aside. Add celery, carrots and onions into the pot with a splash of chicken stock. Cook 5 minutes, stirring and scraping any brown bits from the bottom. Add the tomato paste and let it sit for one minute to carmelize, then stir into the veggies. Add garlic and cook one minute. Stir again. Add chicken stock and butter. Replace ribs back into the pot along with any resting juices. Secure lid and turn off saute setting, making sure the quick release vent is set to closed. Turn pot to high pressure cooker for 50 minutes. Allow the pressure cooker to release naturally for at least 15 mintues. At that point you can either conitnue to let the pressure completly release naturally or carefully move the quick release to open. Once the pressure is gone, carefully remove the lid. Using a slotted spoon, take the ribs out of the pot. Turn on high saute setting and sprinkle the xanthan gum into the broth and whisk together. Cook for 5 minutes until the sauce has thickened and reduced. Serve by plating the ribs and spooning lots and lots of sauce over the ribs. Eat with any keto veggie.