Heat oven or grill to 400 F.

Use half of the butter and heavily grease a cookie sheet.

Add 12 slices of bread to the cookie sheet, top bread with shredded Monterey Jack and cheddar then top with remaining bread.

Heavily grease the other sheet pan and place it on top.

Bake for 10 minutes, carefully flip over the sheet pans while pressed together and bake or grill for another 5 minutes.

Remove from oven or grill, loosen the edges of the sandwiches if the cheese is sticking to the pan, then flip onto a cutting board. Serve whole or slice into halves and serve.