Here's the thing about that. Manufacturers and marketers must take greater care with unsalted butter. The salt gives them some wiggle room that is unavailable with unsalted butter. You are guaranteed that your unsalted butter is fresh.
They put the butter on the top toasted bun and let it drip down through sweated onions and American cheese. The meat patties are thin.
Skip to 2:30 if you care to watch, where they start making burgers, they're yakking it up unproductively before that.
This is Solly's Grille, the place that America's Test Kitchen based their butter burger tests on. The lithe sylphlike cook and the svelte owner insist on outrageous quantity of butter sufficient to drown any insect drawn to it right there on your plate. Pointless when so much of it drips off.
This here is a link to Food Network, a Diners, Drive-Ins and Dives episode showing Crest's butter burger. This is the best of the lot. The cook has 1/3 LB of beef, it looks like to me, gouges out a small portion, inserts a generous pat of compound butter and replaces the gouged portion of meat, smashed the ball into a patty and grills the patty as a steak. The cook says, "broiler." The butter that the cook prepares in advance has generous fresh herbs added to it. Quite a combination here. My favorite things.
So there is no butter soaking the bun. It's all inside the burger. In my opinion, this is the way to go. His is the only burger herbed up, and that combination sounds tremendous.
No cilantro. The most popular herb around here. Man, there sure are a lot of anticilantroites out there. Have you noticed that? It's actually a genetic predisposition. A lot of people just flat cannot stand it. It tastes like soap to them. One guy said, "Is that the stuff that tastes like wet socks?" And I'm all, "What?"