Start by taking your two slices of sourdough bread. Lay them flat on a clean surface and spread 1 tablespoon of softened butter on one side of each slice.
On the unbuttered side of one slice, sprinkle the freshly grated Parmesan cheese evenly. Then, add the freshly grated cheddar cheese on top.
Place the other slice of bread on top, buttered side facing out.
Preheat your non-stick skillet over medium heat. Once it’s hot, carefully place the assembled sandwich in the pan.
Let the sandwich cook for about 3-4 minutes, or until the bottom is golden brown.
Before flipping the sandwich, sprinkle the extra cheddar cheese in a thin layer around the edges of the sandwich in the skillet.
Carefully flip the sandwich over and grill for another 3-4 minutes.
Once both sides are golden brown and the cheese is melted, remove the sandwich from the skillet. Let it cool for a minute, slice it in half, and enjoy!