Prepare burger bun by laying toppings on bottom half of bun. Have it nearby and ready for when your burger is cooked.
Preheat a large stainless steel saute pan or skillet over high for 2 minutes. Place burgers, and smash down with a stiff metal spatula, using a second spatula to add pressure. Smashed patties should be slightly wider than burger bun.
Cook until patties are well browned.
Flip patties and immediately place a slice cheese over 1 patty, then stack the second directly on top, and put another slice of cheese and let the cheese melt.
Melt 2 tablespoons butter and coat the burger bun. Heat a grill pan and toast the buns.
Immediately remove from pan and transfer to waiting burger bun. Serve with favorite toppings- mayonnaise, ketchup, pickles, onions, mustard, tomatoes.