Combine basil, garlic, pine nuts, parmesan, and olive oil in a food processor. Process until well combined.
Grilled Cheese Sandwiches
Spread 1/2 Tablespoon butter on one side of each slice of bread.
On non-buttered side of each of 4 slices of bread, spread 1-2 Tablespoons pesto. Top with 1 slice of mozzarella. Top with remaining slices of bread, butter side out.
Heat skillet over medium heat until hot. Add sandwiches (1-2 at a time, depending on how large of a skillet is being used) to hot skillet, butter side down.
Cook 2-3 minutes or until golden brown. Flip sandwich and cook 2-3 minutes on other side or until golden brown and cheese is melted. Remove from skillet. Keep warm, and repeat with remaining sandwiches.