Line a 9×13″ pan with parchment and lightly grease it/spray it with nonstick cooking spray.
In a large pot, melt the butter over medium-low heat. Add the bag of mini marshmallows and stir until smooth. Remove from the heat and stir in the vanilla extract.
Quickly fold in the Rice Krispies cereal, followed by the crushed graham crackers, 1 cup mini marshmallows, and finally the M&M’s. Stir until just combined (don’t overmix or the M&M’s may melt and bleed).
Press the mixture into the pan using a spatula or spoon sprayed with cooking spray. I like to lightly flatten them with a fondant smoother found- here. While still slightly warm, press the sprinkles into the top of the treats.
Let them cool completely at room temperature before slicing into squares.