Pour biscuit crumbs into a large bowl along with the Rice Bubbles and 3/4 cup halved Maltesers.
In a saucepan over medium heat, add butter, condensed milk and cocoa. Whisk until melted together and smooth. Cook for 1 minute.
Pour over dry ingredients and mix until combined.
Press firmly into tin.
Break white chocolate into a bowl and heat in microwave in 30 second bursts, stirring each time until smooth. Pour over slice.
Press remaining Maltesers into the chocolate.
Please note that if you intend to refrigerate or freeze the slice for longer than 1 day, press the Maltesers into the chocolate with the cut side down. They will stay crunchy. Refrigerate/freeze until set.
Tips: to keep your white chocolate glossy and stop it from cracking, add 1 tablespoon melted copha to the melted chocolate prior to pouring onto slice.