Prepare a 9x13 inch baking dish with nonstick spray and set aside.
Put chocolate chips, corn syrup and 3 TBS butter in a medium sized microwave safe bowl. Microwave for about 2 minutes until soft.
Stir chocolate mixture until all chunks are gone and mixture is creamy. Set aside.
Put marshmallows and butter in a large pot over medium heat.
Melt, stirring often, until marshmallows are completely melted and gooey.
Add chocolate and graham crackers to the marshmallow in the large pot and stir to combine.
Remove from heat and toss in a few extra marshmallows and chocolate chips if desired.
Pour mixture into prepared 9x13 inch pan.Top with additional marshmallows and chocolate chips if you want.
Allow to set before cutting and serving.