Last week on the Viet World Kitchen Facebook page, Jeff Brennan challenged me to create a mayonnaise that contained the flavors of Vietnamese banh mi sandwich. It should be good enough to use for a grilled burger, he wrote. I keep a running list of recipe requests and get to them as my schedule permits. Scott’s seemed doable and quick. Plus, I had some grass-fed hamburger leftover in the fridge. So I tackled the Vietnamese-American burger over the weekend.