Thoroughly wash the oxtails using white vinegar and water. Rub the excess debris off of them. Rinse well and set aside.
Add the olive oil, cilantro, onion, and garlic cloves to a blender. Blend on high for 1-2 minutes until everything is blended together. Add water one teaspoon at a time to loosen-up the mixture if needed.
In a large bowl, pour the marinade mixture over the oxtails, and rub it all around the meat using hands or utensils. Ensure they are coated evenly. Cover the bowl with plastic wrap or an airtight lid and refrigerate for at least one hour, up to 24 hours.
Stewing the Oxtails
Preheat oven to 350 degrees. Remove the oxtails from the refrigerator. Add the seasoned salt, onion powder, garlic powder, and black pepper to them. Mix well until they are fully coated with the seasonings.
Preheat a deep cast iron skillet or stock pot over medium-high heat. Add one tablespoon vegetable oil to the pan.
Place the oxtails in the oil and sear on each side for 3-5 minutes, or until a golden crust is achieved all around.
Pour the beef broth over the oxtails. Add the baby carrots and cover the skillet or pot with aluminum foil and transfer it to the oven.
Let the oxtails braise in the oven for 4-5 hours. Check every hour to ensure the liquid is still covering the oxtails; if not, add water until it is just covering them.
Check to make sure they are fork tender, and remove the skillet or pot from the oven. Prepare the gravy
Gravy
In a large cast iron skillet or stock pot, bring 2 tablespoons of vegetable to the smoking point over medium heat. Add the sliced bell pepper and onions and saute until they are semi-soft, about 5 minutes.
Slowly begin to add the flour, one tablespoon at a time, directly into the pepper mixture. Continue adding the flour until the oil is absorbed by the flour.
Next, whisk in the red wine and cook for one minute. Now begin to slowly pour in the beef broth. Use any remaining broth from the stewed oxtails, and add more if needed to get to the 4 full cups.
Continue whisking vigorously to help break up the bits of flour. The mixture should start to thicken now.
Stir in the tomato paste, and all of the seasonings at this time. If gravy starts to get too thick (to where it is sticking to the spoon or bottom of the pan), add water 1/4 cup at a time to help loosen it up.
Rinse the butter beans and add them to the gravy. Next nestle the oxtails back into the pan with the gravy as well.
Adjust the seasonings as needed at this time. Enjoy!