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!