Spread 1 tablespoon mayonnaise on each slice of bread.
Place 1 slice of cheese over the side of the bread with the mayonnaise, then 3 slices of tomato.
Top with remaining bread slice (mayonnaise side facing in).
Butter the outside of each slice of bread with about 2 teaspoon butter per slice (or to taste).
Heat about 1 tablespoon or more of butter in a skillet over medium heat.
Using a spatula place the sandwich into the skillet.
When the cheese has started to melt carefully flip the sandwich over and continue cooking until both sides are golden brown and the cheese has melted (adding in a little more butter to the skillet if needed).