In a large saucepan with a top, warm the oil over medium-high heat.
Add the onion and garlic and sauté for a couple of minutes.
Add the clams, rice wine, lime juice, fish sauce, and chiles, if using.
Cover and steam for a couple more minutes, until the clams have opened up.
Add the butter and basil and stir.
Try the sauce, adding more lime juice or fish sauce to taste.
Serve immediately.
