Shake the can of coconut milk or stir it well (this creates a consistent thickness, since the fat often solidifies at the top of the can).
In a 3- to 4-quart saucepan or wok over medium heat, simmer 1/2 cup of the coconut milk, stirring occasionally, until reduced by about half, 3 to 5 minutes. It will get very thick and shiny and may or may not separate; either is fine.
Add the curry paste, whisk well, and cook, continuing to whisk, for 1 minute. Whisk in the broth, sugar, fish sauce, and remaining coconut milk. Bring to a simmer over medium-high heat.
Add the green beans, onions, lemongrass, and lime leaves and continue to simmer, adjusting the heat as necessary.
After 2 minutes, add the tofu, bell peppers, and oyster mushrooms and continue to simmer until everything is tender and cooked through, about 3 more minutes.
Remove the curry from the heat. Season to taste with more sugar and fish sauce and stir in the basil. Transfer to a serving bowl (or serve right out of the pot). Remove the lemongrass and lime leaves or tell your guests to eat around them. Garnish with the lime wedges.
nutrition information (per serving):
Photo: Scott Phillips