How to Make It
In a food processor, combine the lemongrass, shallot, ginger, garlic, turmeric, guajillo, Thai chiles and 2 teaspoons of salt. Puree until a chunky paste forms; scrape down the side of the bowl as needed.
In a medium saucepan, heat the peanut oil until shimmering. Add the paste and cook over moderately low heat, stirring frequently, until browned, 10 minutes. Add the sugar and cook, stirring, until melted, 3 minutes. Stir in the coconut milk and bring to a simmer. Cook over moderately low heat, stirring occasionally, until slightly reduced, 10 minutes. Whisk in the peanut butter and cook, whisking occasionally, until thickened, 10 minutes. (The sauce may look broken.)
Remove the sauce from the heat and gradually whisk in the water until creamy and smooth. Season with salt and let cool completely. Garnish with the mint and serve with raw vegetables.