Heat the non-stick skillet over medium heat.
Spread 2 tablespoons of basil pesto on one side of each slice of bread.
On the unpasted side of 2 bread slices, place 2 slices of cheese each. Sprinkle a little salt and pepper over the cheese if desired.
Top with the remaining 2 slices of bread, pesto side facing down, creating two sandwiches.
Add 1 tablespoon of butter to the skillet. Once melted, carefully place the first sandwich in the skillet. Cook for about 3-5 minutes until golden brown.
Carefully flip the sandwich with a spatula, adding the remaining tablespoon of butter to the pan before placing the second sandwich in.
Cook the second sandwich for another 3-5 minutes until both sides are perfectly crispy and the cheese has melted.
Remove the sandwiches from the skillet and let them cool for a minute. Slice in half and serve warm.
Customize with additional ingredients like sliced tomatoes or spinach if desired.
Store leftover pesto in the fridge for use in other dishes like pasta or salads.