Start by pouring the mayo and sour cream into your blender or food processor. Next, add the jalapeño juice, chopped jalapeños, and all the dry spices. Adding the wet ingredients first helps everything mix well.
Put the lid on and blend for 20 to 30 seconds. You want a smooth, creamy sauce without any chunks. If you are using a bowl and a whisk, make sure the jalapeños are very finely chopped before mixing.
Use a spoon to taste the sauce. If you want it spicier, add more jalapeños or a little more chili powder. If it tastes too tangy, add a tiny pinch of sugar. If it’s too thick, a splash of jalapeño juice will help.
Pour the sauce into a sealed jar or container and let it rest in the fridge for at least 30 minutes. This waiting time allows the spices to mix and enhance the flavor. The sauce tastes better after it sits.