I start by softening my butter so it spreads without tearing the bread. If I'm in the mood for extra flavor, I mix in the minced garlic and dried herbs right into the butter. Then I spread it generously on one side of each bread slice, making sure it reaches every corner.
Next, I lay two bread slices butter-side down in my cold skillet before turning on the heat. I place sliced mozzarella on one slice and sliced brie on the other, keeping the rind intact since it holds everything together as it melts. This layering trick keeps the cheeses from mixing awkwardly before they're fully gooey.
I turn the heat to medium-low and let the sandwich halves cook for about 4-5 minutes per side. Going low and slow here is key, because brie needs a little extra time to soften all the way through without scorching the bread. I keep an eye on the color and adjust the heat if it's browning too fast.
Once both cheese-topped slices look melty and the bread is golden, I flip one slice onto the other to form a complete sandwich. If the center still feels a bit firm, I cover the skillet with a lid for about a minute so the trapped heat finishes softening the brie.
Finally, I move the sandwich to a cutting board and let it rest for thirty seconds before slicing. This tiny pause keeps the cheese from spilling out everywhere the moment I cut into it, though a little oozing is honestly part of the fun.