Spray an 8x8 baking dish liberally with non stick spray then set aside. Place 1 cup chocolate chips in a microwave-safe bowl then microwave in 20 seconds increments, stirring between increments, until melted and smooth. Set aside. Place marshmallow fluff in a microwave-safe bowl then set aside.

Melt butter in a large pot over medium heat. Add marshmallows then stir until smooth. Add Rice Krispies then stir until well combined. Working quickly, scoop half of the mixture into the prepared baking dish then press into an even layer (I spray the bottom of a glass with nonstick spray to help press.) Pour melted chocolate over rice krispie treats layer then smooth with a spatula. Add 9 of the graham cracker halves on top. Microwave marshmallow fluff for 20 seconds then spread on top of graham crackers.

Spoon remaining rice krispie treats on top of marshmallow fluff layer then press lightly to smooth. Melt remaining 1/2 cup chocolate chips with vegetable oil in a microwave-safe bowl in 20 second increments, stirring between increments, until melted and smooth. Drizzle on top of rice krispie treats. Crumble 3 remaining graham crackers halves then sprinkle on top. Allow rice krispie treats to set for 30 minutes before slicing into 16 squares with a sharp knife and serving.