Prepare a quarter sheet pan or 9x13 dish by lining the bottom with graham crackers. Measure out marshmallows and chocolate chips and have them nearby.
In a heavy saucepan, melt butter. Add sugar and cook over medium heat, stirring constantly, until it reaches the color of a brown paper bag. Mixture may separate or look curdled, and this is normal.
Pour candy over the graham crackers, trying to coat evenly.
Quickly sprinkle marshmallows and chocolate chips on top, letting them sit a minute or two to melt. Use a toothpick or knife to swirl topping.
Let candy cool for 15-30 minutes, then chill in fridge to let it set. Cut or break into pieces before serving.