Cook the potato in a medium saucepan of salted boiling water just until tender, about 5 minutes. Drain.

In a large saucepan, cook the pancetta over moderate heat, stirring occasionally, until light golden, 7 to 8 minutes. Add the fennel, garlic and green curry paste and cook, stirring, until fragrant, 1 minute. Add the wine and simmer until reduced by half, about 2 minutes. Add the coconut milk and lime juice and return to a simmer. Add the potato, Manila clams and the chopped clams and their juices. Cover and cook until the Manila clams open, 5 to 7 minutes. Discard any clams that do not open. Season the chowder with salt and pepper. Garnish with cilantro, basil and rau ram and serve warm.