01 -
Heat a frying pan over medium-low heat.
02 -
Spread butter evenly on one side of each sourdough slice.
03 -
Place the bread slices butter-side down in the heated pan.
04 -
Layer mozzarella slices on one bread slice, then spread basil pesto over the cheese.
05 -
Add sun-dried tomatoes and cooked bacon slices if using.
06 -
Top with remaining mozzarella slices and cover with the second bread slice, butter-side up.
07 -
Gently press the sandwich and cook until the bottom is golden brown and cheese begins to melt, approximately 3 to 4 minutes.
08 -
Turn the sandwich over and continue cooking until the other side achieves a golden brown crust.
09 -
Remove from heat, allow to rest briefly, then slice and serve warm.