Pre-heat your grill to 450-500°.
Peel back and trim outer layer of Vidalia skin, cutting off the top and the bottom of onion so that it can sit upright.
Place onion on a sheet of aluminum foil and season generously with kosher salt.
Place one teaspoon of sugar on top of the onion (this should look like a little mound of sugar).
On top of sugar, add a pat of butter (Ina always used unsalted).
*Optional* If you'd like, before closing the pocket, drizzle a high-quality balsamic vinegar over your onion (click here for the one that Jule's family cannot live without).
Bring up the sides of the aluminum foil, wrapping your onion.
Pinch your aluminum foil pocket closed with your fingertips, and place directly onto a heated grill grate. If you have an upper shelf, Jule likes to rest them there. They'll need approximately 45 minutes to an hour, depending on their size. You can check them at 45 minutes; they should be fork-tender and starting to blacken. Don't be afraid to allow them to go for an additional 15 minutes. Remember, onions are sweet but tough, just like Ina.