Grease a 9x13 pan with butter and set it aside.

Roughly chop the Cadbury eggs with a knife. Do this slowly and be careful. Leave some whole and various sizes. Some large pieces some small.

Once chopped measure half a cup of them and place them into another bowl for putting on top of the rice Krispie squares later, set aside.

Add the large marshmallows to a bowl and set them aside.

Set 2 cups of mini marshmallows in a bowl and also set them aside. 

Add the rice Krispies to a large bowl and set aside.

In a medium pot on medium low heat add in the butter and melt. Once it is melted, add in the large marshmallows only. Use a rubber spatula and stir until they are just melted. As soon as they are melted remove from the heat. This takes a bit of time but don't be tempted to crank up the heat. 

Stir in the vanilla. 

Add the melted marshmallows to the rice Krispies and mix until blended well. 

Add in the mini marshmallows and then the Cadbury mini eggs, but don't add the 1/2 cup you set aside. Gently fold them in.

Add it all to the buttered pan. Add a little butter to your rubber spatula.

With your greased spatula press it into the pan. 

Add remaining mini eggs on top and press them into the top. Add sprinkles if wanted and gently press those in as well.

Allow to set at room temperature for at least 30 minutes before slicing.

Slice into squares.