Whisk together ½ cup of low-fat mayonnaise with 1 tablespoon of Dijon mustard, season with a little salt and pepper, then taste. Adjust the amount of mayo or mustard to your liking.
To make ours a little lighter and healthier, we used half mayo, half plain no-fat Greek yogourt.
Take ½-1 chile from a can of chipotles in adobo sauce, along with a little of the sauce. Mince finely. Mix into a cup of light mayo (or use ½ cup mayo and ½ cup light sour cream or plain low-fat Greek yogourt). Add salt and a squeeze of lime juice. Taste and adjust seasonings to your liking, adding more minced chipotle if you like it hotter.
This mayo is also great on tacos.