Heat oil in a pot over medium heat.

Sauté the onion, garlic, and tomatoes until the onion becomes soft and translucent.

Add the beef sirloin and cook until nicely browned on all sides.

Pour in the water and bring to a boil. Lower the heat and let it simmer for 30–45 minutes, or until the beef is tender.

Stir in the instant tamarind soup base until well combined.

Add the cubed potatoes and simmer until the potatoes are cooked through.

Season with patis and pepper to taste. Adjust seasoning as needed.

Drop in the finger chilies, if desired, and simmer for another 30 seconds.

Serve hot as a comforting soup, or enjoy with steamed rice.