Step 1: Cook the bacon in a large skillet over medium heat until crispy. Remove to a paper towel-lined plate to drain excess grease. Once cooled slightly, you can break it into smaller pieces if desired.
Step 2: While the bacon cools, grate all three cheeses (if not already shredded) and combine them in a small bowl.
Step 3: Spread butter or mayonnaise evenly on one side of each slice of bread. This will be the exterior of your sandwich.
Step 4: Place two slices of bread, buttered-side down, in a cold skillet or on a griddle. Immediately layer half of the mixed cheese on each bread slice in the pan.
Step 5: Top the cheese with 4 slices of crispy bacon on each sandwich (or crumbled bacon), then add the remaining half of the mixed cheese over the bacon. Place the other two slices of bread on top, buttered-side up.
Step 6: Cook over medium-low heat for 4-6 minutes per side, or until the bread is golden brown and the cheese is thoroughly melted and gooey. Press gently with a spatula occasionally to ensure even contact and melting.
Step 7: Remove from heat, let cool for a minute, then slice in half diagonally and serve immediately for the ultimate cheesy, bacony delight!