In a medium bowl, combine the jicama, chayote, red onion, bell pepper, jalapeños, mayonnaise, buttermilk, lime juice, Dijon mustard, salt, sugar, and cayenne. Mix well and refrigerate for at least 1 hour and up to overnight.
Note: If you don’t have buttermilk on hand, you can make your own by adding 1 tablespoon distilled white vinegar to 1 cup whole milk. Stir to blend and set aside until thickened and creamy, usually about 5 minutes; then use as needed.
Yield: About 1 generous quart