Curries in Thailand are light and soup-like as compared with the rich, thick curries of India. They are always served as part of a selection of dishes in a main meal and rarely on their own.
In large wok or skillet, heat oil over medium-high heat. Add onion and stir-fry until golden, 5 minutes. Add curry paste and stir-fry 1 minute. Add potatoes and toss well to coat. Stir in coconut milk and broth.
Using your hands, lightly crush tomatoes; add tomatoes and juice to wok. Cover and simmer until potatoes are tender, 15 to 20 minutes. Stir in lime juice and basil. Serve over rice with sambal oelek if desired.