From Flavors of Home by Alix Wall
“I always get a lot of questions on how to use lemongrass. The most common remark is, ‘I never seem to extract the lemongrass flavor.’ My answer is that you have to use a lot of lemongrass, and that you will either have to bruise the stalk or chop it very finely.
“People also ask, ‘Which fish sauce do I use? How do I apply it?’ I prefer Three Crab brand fish sauce for adding to sauces that won’t be cooked, since the brand seems to lose its salty flavor with long cooking. Squid brand fish sauce is saltier and is great for marinades.” —Chef Tu David Phu
1 stalk lemongrass
3 tablespoons Squid brand fish sauce
1 tablespoon organic sugar
5 whole garlic cloves, peeled
1 pound filet mignon, tri-tip, or skirt steak
Prepare lemongrass by cutting away the bottom half inch of the stalk. (This part is very woody and should be saved for broths or soups.) Cut the stalks into ½-inch segments and chop finely in a food processor. Add garlic cloves, fish sauce, and sugar. Blend to a fine paste, about 1 minute. Place beef into a zip-top bag with the marinade, making sure to coat all of the beef. Seal and marinate overnight or 8 hours*. Remove the beef from the refrigerator 30 minutes before cooking. Drain away marinade before cooking to your liking. Letting the beef rest for about 10 minutes before slicing will help it retain the juices.
*Note: If you have a sous vide machine, there’s no need to marinate. Set machine and water to 140° and let it sit for 2 hours. Then cook to your liking.