This is Vietnamese street food from friend and Chef Kevin Do. Bắp Nướng Mỡ Hành is the late-night grilled corn you find at vendor carts in Saigon, Hanoi, and pretty much everywhere in between. Corn gets charred hard over hot coals, then drowned in scallion oil and brushed with a sticky fish sauce glaze that caramelizes in the last two minutes. Sweet, savory, smoky, allium-forward.
The technique splits depending on the corn you've got. Vietnamese waxy corn (sometimes sold as glutinous or sticky corn) goes naked on the grates and chars directly. American sweet corn gets steamed in its husks first, then peeled back for the char. Either way works. The scallion oil and the glaze do the rest.