Spread a thin layer of butter on one side of each bread slice. Place one slice, buttered side down, onto a cold skillet.
Add slices of provolone cheese evenly over the bread in the skillet. Cover with the second slice of bread, buttered side up.
Turn on the heat to medium and cook the sandwich for 2-3 minutes, until the bottom is golden brown and crispy. Lightly press with a spatula for even contact.
Carefully flip the sandwich using a spatula and cook the other side for another 2-3 minutes until golden brown and the cheese is fully melted. You should see bubbling cheese and a crisp crust.
Remove the sandwich from skillet once both sides are evenly browned and cheese is thoroughly melted. Let it rest for a minute before slicing if desired.
Slice and serve immediately, allowing the cheese to be warm and gooey with a crispy crust on the bread.