Spread the butter evenly on one side of each bread slice.
Place one bread slice, buttered side down, onto the preheated skillet over medium heat.
Layer the provolone cheese evenly over the bread in the skillet, then top with the second bread slice, buttered side up.
Cook for about 3-4 minutes, until the bottom is golden brown and crispy; gently lift the edge to check the color.
Carefully flip the sandwich using a spatula and cook for an additional 3-4 minutes, until the second side is golden brown and the cheese begins to melt and bubble.
Remove the sandwich from the skillet once the cheese is melted, and the bread is evenly browned. Let it rest for a minute, then cut in half and serve hot.