Heat a large cast-iron or non-stick skillet over medium-high heat. While your pan is heating up, spread the butter on each slice of bread, one side only. Mix the gochujang with the sesame oil and spread that on one slice of bread (on the opposite side of the butter).
Place the first slice of bread, butter side down, into the hot pan, top with the cheese, and then place the other slice of bread on top, gochujang mixture touching the cheese, butter side out. Cover the pan with a lid and let cook for about 3 to 4 minutes, or until nicely browned.
Remove the lid and flip the sandwich to brown the other side. You don't need to place the lid back on; at this point, the cheese should already be nice and melty. Remove from the heat and enjoy while hot.
Notes
*I love using a good, artisan sourdough (Miche Sourdough), or good-quality crusty Italian bread. You can also absolutely use white sandwich bread. **You can use freshly grated, shredded or slices. I used a combination of cheddar + colby jack but you can really use any cheese you like: sharp cheddar, mozzarella, fontina cheese, Gruyère, white cheddar, whatever you like in a grilled cheese! I really think the gochujang goes with anything!