Cut a sheet of aluminum foil to fit the interior of your toaster oven. This will catch any cheese drips during cooking.
Butter one side of two bread slices and place them buttered-side down on the foil. Completely cover the bread with cheese slices.
Place sandwiches in the preheated toaster oven and toast for 3-5 minutes, until cheese starts to melt.
Butter one side of two more bread slices and place them buttered-side up on top of the cheese.
Toast sandwiches for 5-7 minutes, until the top bread is lightly browned.
Use tongs to carefully flip sandwiches then toast for another 5-7 minutes, until the second side browns.
When both bread sides are crispy and brown, remove the sandwiches from the toaster oven. Let cool slightly, cut in half, and enjoy your grilled cheese!