Step 1

In a medium saucepan, whisk 1/4 cup of the coconut milk with the curry paste. Stir in the remaining coconut milk, the stock, lemon zest, ginger, lime zest, 2 tablespoons of the fish sauce and the brown sugar and bring to a simmer. Cook the sauce over moderately high heat until reduced by one-quarter, about 15 minutes.

Step 2

Using a slotted spoon, remove the lemon zest, ginger and lime zest and discard. Stir in the lime juice, cilantro, basil and the remaining 1 tablespoon of fish sauce; transfer to a bowl.