Not the original recipe, but nowadays the defacto "real" margarita for tequila lovers. The original was intended to cover up the taste of cheap
tequila, the purpose of the modern recipe is to showcase the flavor of the tequila, so whatever you do don't use cheap
nasty tequila! Real tequila will say 100% agave on the label.
2 parts Tequila
2 parts fresh squeezed lime juice
1 part agave nectar
You can blend it, if you must, salting the glass is also not really recommended. Shaking is the preferred method of mixing. Shake vigorously for about a minute, you need some ice melt to dilute it otherwise it is a little strong.
Agave nectar is increasingly available at grocery stores as an alternative sweetener. It is much healthier than sugar, it has a lower glycemic index, which is good for diabetics, I guess. I have found the lighter the color the better it is for margaritas. You used to only find it at health food
and gourmet stores, now I find it at major chains like Safeway and even at Costco! Surprisingly the local Mexican supermarket does not carry it.
Many people have strong opinions about the use of Mexican limes, which are smaller than the Persian limes, which are the default breed seen here in America. I cannot discern a significant difference in any of the lime varieties I have experimented with, other than "sweet" limes which are completely different, and have a flowery sweet citronella like flavor. I encourage you to experiment
with different limes, I'm sure results will depend more upon what grows well where you are than the breed. I like to mix 1 sweet lime with every 6 Persian limes for a really nice flavor that keeps people guessing.
My one piece of advice regarding limes is to experiment
with the degree to which you squeeze them. After I squeeze the limes, I put two "pre-squeezed" lime rinds in the squeezer and squeeze them again. This releases additional aromatic oils from the skin. These oils enhance the lime flavor, but too much can be bitter, and sometimes it makes me burp lime taste, so you really have to watch the balance. Getting it right takes your margarita to an awe inspiring level.
Since this recipe showcases the flavor of the tequila, you need a good quality tequila, or no matter what, your margarita will suck. There are 3 grades of real tequila plata (silver), reposado(rested), and anejo(aged). Here are basic recommendations for all 3 grades.
Silver- Avion. Big winner at 2012 SF international Spirits Competition
Sorry-but as far as I know the next two are only available in Mexico
Reposado- Herradura Antiguo. You may think you have seen this outside of Mexico, but TRUST ME it is not the same. The one you get in Mexico is better.
Anejo- Tapatio. Tapatio anejo kicks ass, and it's cheap too. Some snobs will say anejo is too good for mixing in cocktails, and should only be sipped straight. Blah blah blah, I can only imagine how much of a fit they would pitch
over my Pappy Van Winkle 20 year Manhattan! In a cocktail that showcases rather than covers up the flavor of the liquor, it pays to use the very best.
Since the OP asked for my favorite recipe, I would have to choose Don Julio 1942 for the tequila in my absolute favorite margarita, which at $100 a bottle is just a tad extravagant, even for me.