Combine the basil, cooled pine nuts, cheese, lemon juice, garlic, and salt in a food processor or blender. With the mixer running, drizzle in the olive oil in a slow stream until well blended.
Taste and adjust seasoning...you might want more garlic, more salt, more lemon juice. Whatever you feel it needs. Go crazy!
Put some pesto aside for our yummy sandwiches, and store the rest in a jar in the fridge for one week, or in the freezer. If you are freezing, freeze it in an ice cube tray then transfer to a freezer safe bag so you can defrost individual portions as needed. This has saved me many a day when I had no idea what to eat!
For the grilled cheese, sprinkle some mozzarella cheese on one piece of sourdough bread (or bread of your choice). Sprinkle some shredded cheddar cheese on top, then spread a thick layer of pesto on another slice of bread. Sandwich the two slices of bread together.
Heat a skillet over medium heat, and add about 1 tablespoon of butter. Wait for it to heat up really well, then place your sandwich in the skillet. Let it cook, patiently, until it's golden brown, then flip to the other side and repeat.