Preheat broiler and position rack 6 inches from heat source.
Stir butter, mayonnaise, garlic powder, salt, and pepper in a bowl until smooth.
Fold in half of the cheddar and all the mozzarella.
Spread mixture evenly over bread slices, edge to edge.
Top with remaining cheddar, pressing lightly so it adheres.
Broil until cheese bubbles and edges turn golden, 4–6 minutes.
Shower with parsley, slice if desired, and serve hot.
Notes
Try a sprinkle of red pepper flakes for heat or swap in Monterey Jack for extra melt. Leftovers reheat well under the broiler for 1–2 minutes.This recipe is an original creation inspired by classic Cheese Toast Delights flavors. All ingredient ratios and instructions are independently developed.