Cilantro Lime Sauce

Steps

1. Swish the cilantro in a bowl of cold water to loosen any grit, then spin or pat it very dry in a towel: water left on the leaves would thin the sauce. Trim only the bottom 3/4 inch (2 cm) of the stems, which tend to be gritty and woody, and roughly chop the rest, stems included.
2. Finely grate the zest of one lime, avoiding the bitter white pith. Then juice both limes: you need about 3 tablespoons of juice.
3. Peel the garlic clove. Halve the jalapeño lengthwise, scrape out the seeds and white ribs for a mild sauce or leave them in for more heat, then cut it into chunks.
4. Put the lime juice, garlic and jalapeño in a food processor or blender. Blend for 10 seconds, until the garlic is a smooth purée with no pieces.
5. Add the cilantro, sour cream, mayonnaise, lime zest, honey, the pinch of cumin and the salt. Blend 30 to 45 seconds, scraping down the sides once, until the sauce is smooth, soft green and flecked with dark green specks.
6. Check the texture: it should coat the back of a spoon and fall off in a ribbon. Add the cold water 1 tablespoon at a time, blending 5 seconds after each, until it reaches the consistency you want: thicker for tacos, looser for drizzling over a bowl.
7. Taste and adjust: a pinch of salt if it tastes flat, a few drops of lime juice if it needs more brightness.
8. Pour the sauce into a jar, cover and refrigerate for 15 minutes before serving: the flavors meld and the sauce thickens slightly as it chills.