Generously butter one side of each bread slice using ½ tablespoon of unsalted butter. Warm a cast iron skillet or a durable non-stick pan over medium-low heat, or set a griddle to 275˚F. Lay two slices of bread, buttered side facing down, into the preheated pan.

Layer the cheeses starting with cheddar, followed by Havarti, and then Gouda on one slice. Once the bread achieves a golden hue on the underside, place the second slice over the cheese, browned side outward.

Continue grilling the sandwich, turning it once, and pressing it lightly to ensure good contact between cheese and bread. Allow approximately 5 to 6 minutes for the bread to reach a deep golden crust while the cheese melts evenly. Maintain moderate heat to prevent burning and promote gradual melting.

Once both sides are evenly browned and the cheese is visibly melted, transfer the sandwich to a serving plate and slice diagonally. Repeat the process for the remaining sandwiches.