Pesto makes everything better, so spread a generous dollop on this grilled cheese sandwich that's crusted with Parmesan and filled with Gruyére.
Sprinkle Parmesan on the outside of both slices of bread. Heat the bread in the microwave or oven until the Parmesan is melted. Spread pesto on the inside of the slices of bread and top with slices of Gruyére. Grill the sandwich until the cheese is melted and the bread is cripsy.