Begin by laying out two slices of your chosen bread, such as sourdough or whole grain. Generously spread a layer of sun-dried tomato pesto on one side of each slice.

Place a slice of mozzarella cheese on the pesto side of one slice of bread. Top it with the second slice, ensuring the pesto side is facing down.

Heat a skillet over medium heat and add about one tablespoon of butter, allowing it to melt completely.

Once the butter is melted, place the assembled sandwich in the skillet. Grill for about 3-4 minutes until the bottom turns a deep golden brown.

Carefully flip the sandwich using a spatula, and grill the other side for another 3-4 minutes.

Once both sides are perfectly grilled, remove the sandwich from the skillet and let it sit for a minute. Slice in half and serve immediately.