Line a 8x8 or 9x9 inch baking pan with parchment paper, or coat with cooking spray. You can use 9x13 pan for thinner rice krispie treats.
In a large Dutch oven or saucepan, melt butter over medium low heat.
1/4 cup butter
Set aside 1 cup of the mini marshmallows and add the remaining marshmallows into the saucepan and stir until completely melted.
Remove from heat, then stir in vanilla extract.
1 tsp vanilla extract
Add 1 cup of marshmallows, rice krispies cereal, candy coated chocolate, and sprinkles, then gently stir to combine. It's okay if some of the chocolate candy melts, it'll add to the flavor.
6 cups rice krispies cereal, 1 cup candy coated chocolate, 1/4 cup pastel rainbow sprinkles
Transfer to the prepared baking pan. Use a silicon spatula to gently press down until evenly distributed. DO NOT press down too hard or they'll be overpacked and hard once cooled.
Add a few extra candy coated chocolate and sprinkles on top, press down gently, then let the rice krispies treats set for 1 hour.
Remove from pan, cut into squares, and enjoy!