Line a baking pan with parchment paper and set it aside. You can squeeze the parchment paper up into a ball then run it under water and gently dry it off, this will make it more flexible and easier to work with. The parchment paper will make it easier to remove the rice krispies treats and transfer to a cutting board.
Melt the ½ cup salted butter in a large pot over low heat.
Set 1½ cups of marshmallows aside for later. Add the rest of the 12 ounces mini marshmallows to the pot with the melted butter and continue to melt on low heat, stirring constantly until smooth.
Remove the pot from the heat and fold in the 7 cups Rice Krispies cereal, broken up 1½ cups tiny pretzel twists, 1 cups Mini Cadbury Eggs, and the mini marshmallows that were set aside earlier. Fold together until evenly distributed and coated in the melted marshmallow mixture.
Gently spread the Rice Krispies mix into an even layer in the baking pan with a rubber spatula. Do not press it in too hard otherwise it will result in hard to eat treats.
Melt the ½ cup ghirardelli vanilla melting wafers and ½ cup wilton candy melts separately in microwavable piping bags on a low setting, massaging the bag every 30 seconds, until fully melted.
Drizzle over the prepared Rice Krispies treats and then immediately top with additional chopped Mini Cadbury eggs and Sprinkles.
Allow it to cool on the counter for 30 minutes to 1 hour before cutting into squares.