Add all of the ingredients to a blender and blend on high until everything is combined and emulsified. This should just take 20-30 seconds, depending on the power of your blender. (It's okay if there are still flecks of cilantro, but you don't want any big chunks of jalapeño).
Pour into a glass dish or jar with a lid and store in the fridge for 2-3 days.
Notes
You'll need to use a blender for this recipe. I use the smoothie cup that comes with my blender, but a larger stand blender will work too. If you don't have a blender, a food processor can also work.
When removing the seeds and membrane from the jalapeños, you might want to wear gloves to protect your hands from getting spice burns.
The seeds and membrane of a jalapeño contain more heat than the flesh, so I normally remove them, but you can add them for extra heat if you prefer.
Once stored in the fridge, the vinaigrette may solidify a little and the oil may separate. Just let it sit at room temperature for 15-20 minutes and then shake or stir it before using.