Place two slices of bread on a plate or flat surface.

Cut avocado in half and remove pit. Scoop contents into a small bowl and mash with fork.

Spread avocado evenly onto each bread slice and season with salt and pepper.

Place two slices of cheese on top of the avocado on one slice of bread, then add tomato slices, followed by the third slice of cheese.

Put the second bread slice on top of the sandwich and spread 1 tablespoon of softened butter evenly over the top of bread, coating to the edges.

Heat a small skillet over medium heat and place the sandwich, buttered side down, onto skillet. Butter the slice of bread that is facing up. Cook sandwich over medium heat, 3-4 minutes per side, or until crust is golden and cheese starts to melt.

Remove from heat and serve immediately.