1 Measure out 1 TBL of the vegetable broth and set it aside in a small glass. 2 Put the rest of the broth in a small saucepan and bring it to a simmer. Add the curry paste, lime zest, lime juice, ginger, peanut butter, sugar, soy sauce, and garlic. Mix it all up and make sure there aren’t any curry or peanut butter chunks. 3 Mix together the cornstarch with the broth you put in the small glass until there are no more chunks. This is going to thicken up that watery-ass sauce, just wait. Pour this into the simmering sauce and whisk until the sauce starts getting nice and thick, about 1 minute. Turn off the heat, taste, and add more garlic, lime juice, or whatever your tongue is craving. Let it cool for at least a couple minutes before serving.
See this page for some more about this. Either of these will thicken the out of your sauce.