Divide ground beef into 6 equal sized portions.
Flatten beef into thin patties.
Season beef patties with salt and pepper.
Heat a large cast iron skillet or griddle over medium high heat.
Butter one side of each slice of bread.
One the grill is hot, place beef patties on the grill and fry until cooked through, about 3-4 minutes per side.
Reduce heat to medium and place 3 slices of bread, buttered sides down on the grill.
Top each slice of bread with cheese and two cooked beef patties.
Top beef patties with sliced tomato and a slice of cheese.
Top with a slice of bread, butter side up.
When bread is toasted and golden brown and crisp on one side, use a spatula to flip the sandwich over.
Cook until bread is toasted and cheese is melted. Use spatula to press sandwich together as it cooks.
Serve with mustard, ketchup and sliced pickles if desired.