Seriously it’s the perfect way to do it. You know your pan is hot enough. The butter is nicely browned. I do find a small pan is the right way to keep a good layer but if you have a slightly larger pan using a spatula to keep the butter contained to one space and then put in the grilled cheese while the butter’s still a little solid works too. It’s probably been more than a decade since I last buttered the bread not the pan and I’m not even 30 it’s just the best way.