Line a 9-inch square baking dish with parchment paper. Set aside.

In a medium saucepan set over medium-low heat, combine the butter, brown sugar and honey. Stir until smooth and mixture starts to bubble. Once bubbling, cook for 2 minutes while stirring. Remove from heat and stir in the vanilla.

Stir in the oats, cereal, and graham cracker. Stir until well coated. Let stand 10 minutes to cool. Gently fold in marshmallow fluff until just combined. Pour into the prepared pan. Sprinkle the chocolate chunks over the top and gently press into the granola bars with your hands.

Place the bars in the refrigerator and let cool for at least 30 minutes. Cut into bars and serve.

Store granola bars in an airtight container in the refrigerator with wax paper separating the layers.