Season and sear the oxtail:
Season oxtail pieces with salt and pepper, then dust lightly with flour. Heat oil in a large heavy pot over medium-high heat. Brown the oxtail in batches until well-seared on all sides. Remove and set aside.

Sauté the vegetables:
In the same pot, add onion, garlic, carrots, and celery. Sauté for 5–7 minutes until softened.

Build the stew:
Stir in the tomato paste and cook for 1 minute. Add the chopped tomatoes, beef stock, wine (if using), bay leaves, thyme, and paprika. Return the oxtail to the pot and bring to a gentle boil.

Simmer:
Reduce heat to low, cover, and simmer for 2½ to 3 hours, or until the oxtail is fork-tender and the sauce is rich and thick. Stir occasionally and add a bit of water or stock if needed.

Serve:
Remove bay leaves. Sprinkle with chopped parsley and serve hot with creamy mashed potatoes, rice, or crusty bread.