Lay out the 2 slices of bread. Evenly spread 2 tablespoons pesto over one side of one slice.
Top the pesto with the 2 slices Sargento® provolone cheese. Close the sandwich with the other slice of bread (pesto side facing the cheese) and press firmly to seal.
Heat a medium skillet over medium-low heat. Add 1 tablespoon of the butter and let it melt, swirling to coat the pan.
Place the sandwich in the skillet, buttered side down. Press down gently with a spatula.
Spread the remaining 1/2 tablespoon of butter over the top slice of bread (the side facing up in the skillet).
Cook for about 5–6 minutes on the first side over low to medium-low heat, until the bottom is a golden, crispy brown and the cheese begins to melt. If the bread browns too quickly, reduce the heat.
Carefully flip the sandwich and cook another 5–6 minutes on the other side, until that side is golden brown and the cheese is fully melted. Remove from the skillet, let sit briefly if desired, then slice and serve.