Spray a 9-inch pie plate with nonstick cooking spray. Place Rice Krispies and 1/3 cup sprinkles in a large bowl.
In a medium saucepan over medium heat, melt butter. Stir in marshmallows until smooth and completely melted. Pour over rice krispie and stir to coat completely. Use your hands or the bottom of a measuring cup to press mixture into prepared pie plate making a pie crust for the cake. Set aside to cool and harden.
Remove ice cream from freezer and let soften enough that it’s spreadable. Place in a large bowl and fold in 1/3 cup sprinkles. Place in pie crust and smooth to make even. Freeze pie until ice cream hardens completely, 30 minutes to 1 hour.
Place candy melts in a microwave proof bowl and melt, stirring until smooth. Drizzle over the cake in a cross pattern and top with remaining sprinkles.