This quick sauce will be a little thinner than mayonnaise. We love serving it with asparagus, in lieu of hollandaise. It's also great on sandwiches...a pounded chicken breast, breaded and fried, served with a slather of jalapeno aioli and some cole slaw wouldn't be too bad at all!
This is a "by-hand" method, but you can absolutely make this in a blender.
In a bowl, whisk together the egg yolk, lemon juice, minced garlic, jalapeno and salt. VERY SLOWLY, begin whisking in the oil. Take your time - if you drizzle too quickly, it won't emulsify properly. Once all of the oil is incorporated and the sauce is thickened, stir in the cilantro and check for seasoning.
This will keep in the refrigerator for 3 - 4 days.