Add some Olive Oil (1/2 cup) to the pressure cooker and set to sauté. Add in the Oxtail (4 pound) and sear, seasoning with Ground Black Pepper (1 1/2 tablespoon) and Kosher Salt (1 tablespoon). If needed, sear in 2 batches to avoid overcrowding.
Slice the Vidalia Onion (2).
Halve the Celery (4 stalk) and chop it.
Chop the Garlic (2 clove).
Slice and chop the Green Bell Pepper (1).
Add all the oxtail back to the pot and then add the chopped vegetables. Add the Water (5 cup) and stir. Season with some more Ground Black Pepper (1 1/2 tablespoon) and Kosher Salt (1 tablespoon). Add in the half the Baby Carrots (0.5 pound), place the lid on while making sure the valve is set to "closed". Set to stew and cook for 1 hour.
Once the oxtail is done cooking, remove to a separate bowl and set aside. Set the cooker back to the sauté function. In a small bowl add the Unsalted Butter (6 tablespoon) and All-Purpose Flour (6 tablespoon) and mix together until smooth. Then add to the pressure cooker and whisk to incorporate well.
Add the Potato (10), Tomato Paste (4 tablespoon), Baby Carrots (0.5 pound) and mix everything together. Place the lid back on, and cook using the bean chili function of your pressure cooker for 5 minutes
Set back to sauté and add the oxtail back in. Place the lid back on and let it continue to cook for 5-10 minute. Serve in bowls and Garnish with Fresh Parsley (to taste) before serving.