01 -
Smear butter on one side of all sourdough pieces. Turn them over and put a thin coat of mayo on the other sides.
02 -
Toss together the cheddar, Gruyère, blue cheese (if using), garlic powder, onion powder, thyme, smoked paprika, salt, and pepper until everything's well mixed.
03 -
Lay two bread slices with mayo facing up. Split the cheese mix between them, then cap with the other slices, mayo sides down.
04 -
Warm up a non-stick pan or griddle on medium for about 2-3 minutes until it's nice and hot.
05 -
Put sandwiches in the hot pan and let them cook for 3-4 minutes until they're crispy and golden on the bottom. Keep an eye on them so they don't burn.
06 -
Flip them carefully and cook another 3-4 minutes. Add more butter if needed. They're done when the cheese is all melty and both sides look golden-brown.
07 -
Take them off the heat and let them sit for a minute. Cut each one diagonally and eat while warm. Add some arugula on top if you'd like.