A lot of people like to add fancy cheeses and different ingredients to grilled cheese sandwiches, but to me, there’s nothing more comforting than the classic. Usually, I just add bacon and enjoy my sandwich with a side of tomato soup, but I also love using grilled onions. The key here is using mayo (not butter!) to get the outside of the bread super crispy.
Heat a nonstick pan over medium-low heat.2.
While the pan warms, spread an even coat of mayo on two slices of bread. Place one slice of bread in the heated pan, mayo-side down. Place the slices of cheese on the bread in the pan, cover with bacon strips, then add the grilled onions, if using. Top the sandwich with the second slice of bread, with the mayo-slathered side facing up.3.
Cook the sandwich for 2-3 minutes on one side, until the bottom piece of bread turns golden-brown. Flip the sandwich over and cook for an additional 2 minutes (check to make sure it’s not burning), until the other piece of bread is also golden-brown and the cheese is fully melted.