In medium saucepan, melt butter over medium heat. Once melted, add in marshmallows. Stir continuously until melted.
Line medium mixing bowl with butter. Pour entire bag of Cocoa Pebbles into bowl. Add in marshmallow mixture. Stir until each piece is covered in marshmallow.
Let cool for 5 minutes. While cooling, spray springform pan with baking spray.
Pour Cocoa Pebbles mixture into springform pan. Spread it along the bottom & sides of the pan until completely covered. Press down with your hands to secure Pebbles into place.
While mold is setting, in separate mixing bowl, combine all filling ingredients. Beat with electric mixer until smooth (low-medium speed).
Pour filling into Pebbles pie mold & spread with spatula until smooth.
Refrigerate for 1 hour or until filling & crust have set. Release side of springform, serve, & enjoy!