Add all dry ingredients to a wide, shallow bowl and mix well with a wire whisk. In a separate bowl, add the eggs and beat until well combined, then mix in the buttermilk.
Dredge the onion and jalapeno strips in the egg/buttermilk mixture, then dredge in the flour mixture.
Add half of the strips to the fryer basket, then gently lower into the oil. Shake gently to ensure all strips settle into the oil. Fry for two minutes, then remove to a paper towel lined plate. Repeat with the other half of the strips.
Bring a pot of water to a simmer and add the garlic and arbol chiles. Let soak for 15 minutes. Remove and strain very well.
With a sharp knife, very finely mince the arbol chiles, then go back over them several more times with your knife to mince them as finely as possible. Chop the garlic up, then mash it to a paste with a fork.
Add the minced arbols and garlic to a bowl with the salt and pepper, then thoroughly mash together. Add the sour cream and thoroughly mix, but don't whip it.
Arbol crema can be quite hot for some people. You can use less arbol peppers if you like, or simply give an additional dipping option, like ranch dressing.