Peel the ginger with the edge of a spoon, then grate it on a microplane. Grate the garlic the same way. Grating gives you a smooth dressing with no raw chunks of garlic.

In a medium bowl, whisk the peanut butter, soy sauce, honey, and sriracha. It will look thick and pasty at first, which is normal. Keep whisking about 30 seconds until it looks glossy.

Whisk in the rice vinegar and lime juice, then the sesame oil and neutral oil. The mixture may look split for a moment. Keep whisking until it turns smooth and pale tan. Stir in the ginger, garlic, and fish sauce if using.

Whisk in the warm water 1 tablespoon at a time. You want a dressing that runs off the whisk in a steady ribbon and coats the back of a spoon. For a salad, I stop at 3 tablespoons. For a drizzle over grain bowls, I go up to 4.

Stir in the cilantro and let the dressing sit 10 minutes so the ginger and garlic mellow into it. Then taste it on a lettuce leaf, not off the spoon, since that shows how it will really taste. Too sharp: add 1 teaspoon honey. Too sweet: add 1 teaspoon lime juice. Flat: add a pinch of salt or a few drops of soy sauce. Not spicy enough: add more sriracha, 1/4 teaspoon at a time.