Lightly grease two 12-cup muffin tins with cooking spray and set aside.
In a pot over low heat, melt 4 tablespoons unsalted butter and then stir in ⅛ teaspoon salt.
Add 4 cups mini marshmallows, stirring occasionally until fully melted. Remove the pot from the heat.
Add and gently fold in 5 cups Cocoa Pebbles cereal until completely coated in the melted marshmallows.
Fill each muffin cup with 3 to 4 tablespoons of the cocoa pebbles mixture and then press it into the cup to mold it. Make sure not to press too hard or it can make the treats tough. There should be a small dip in the center to fill with the peanut butter. Let it sit at room temperature for 30 minutes to cool and firm up.
Once the nests have set, divide the 18 tablespoons creamy peanut butter to top each next with 1 tablespoon of peanut butter each.
Add Sprinkles of choice if desired and then divide the 54 mini cadbury eggs to top each nest with 3 mini Cadbury eggs.
Carefully remove each nest with a butter knife or wooden skewer and then place on a serving platter.