Heat 3 tablespoons of olive oil in a pan.
Now, add in the beef oxtail and cook it properly from both sides for 6 about minutes.
In another skillet, heat 2 tablespoons of olive oil. Then, toss in the carrots, onions, garlic, and leek.
Stir all the ingredients until they get tender for about 6 minutes.
In a pot, add the cooked oxtail and vegetable mixture. Then, add wine, thyme, tomatoes, and bay leaves to it and keep stirring.
Bring the mixture to a boil and cook for about 4 minutes.
Now, add 2 cups water along with a bouillon cube, salt, and pepper to it. Cook it over low heat for about 4 hours until the meat becomes soft and separates from the bones.
Remember to remove the oxtail out from the mixture.
Place a skillet over medium heat. Add flour to it. Keep stirring for about 16 minutes until a paste is formed and the flour becomes a little brownish.
Now, add in the stewing liquid and bring it to a boil it. Let it simmer for 3-4 minutes until it gets thick.
At last, pour the stew over the beef oxtail and serve.