Of the favorite burgers in my life, there are two that come on a "French" roll instead of a bun. The first was at Rossati's Roadhouse (generally called "Zot's") in Woodside, up near Palo Alto; it's still being served, though the last one I had was a shadow of its 30-years-ago goodness. The other is to be found at Rotier's in Nashville. And now I've found a very worthy third: it's the Juicy Lucy burger at The Wild Hare in Highland Park. It's a lot like the Zot's burger in that the onions are grilled with the meat, but unlike either of the other two the patty is not made oblong to fit the roll, but is both round and very thick. Very cheesy, too, and yes it IS juicy! And good. I didn't bother to specify its degree of doneness, so I can't report on their flexibility in that department, though I'd expect them to accede cheerfully to any request. It ain't really cheap, I think eight or nine bucks, and it comes with zilch, so you have to get your fries separately...but THOSE are excellent and come with both ketchup and a nice aioli.