Heat a Good Cook Cast Iron Grilled over medium-low heat.
Butter the outside of 2 slices of bread. Spread mayonnaise (or pesto) on the opposite side of 2 pieces of bread.
Place bread buttered-side down in griddle. Top each slice with cheese. Cook until golden. (Cover with a lid or baking pan to speed up the cheese melting process).
Remove from heat. Top 2 slices of bread with sliced heirloom tomatoes and fresh basil (if desired). Place second piece of bread on top. Slice, serve and enjoy!
For extra crunch, add sliced cucumber to the center of your sandwich, too. Delicious!