Butter one side of each slice of sourdough bread.
Spread it evenly to ensure perfect browning.
Place one slice of colby cheese on the unbuttered side of one bread slice.
Add a slice of provolone cheese on top.
Sprinkle a layer of shaved parmesan cheese over the provolone.
Put another slice of colby cheese on top of the parmesan.
Place the other slice of bread on top with the buttered side facing outward.
Press down gently.
Heat a skillet over medium heat.
Grill the sandwich on one side until golden, about 3 to 5 minutes.
Flip and repeat.