Smear butter OR mayonnaise on one side of each sourdough slice. Butter provides a mellower, smooth flavor to the grilled cheese. Mayonnaise provides a slight zing. I personally prefer mayonnaise, but butter is the classic grilled cheese smear.
Slice your cheese into the desired thickness. Chop up basil.
Place a sourdough slice (smeared side down) onto a pan over medium heat. Layer your cheese on the bread to your desired thickness and sprinkle on chopped basil. Cover the cheese with the other slice, leaving the smeared side up.
Cook for about 2-3 minutes. Lift up the sandwich with a spatula and see if the bread is browned. If not, cook for an additional minute and check again. Cook until desired preference and flip.
Repeat step 4 for the other side of the sandwich. When it reaches your desired brown level, remove from the pan and enjoy!