Chop the white chocolate up finely. Line a square 8×8 inch baking pan with baking paper.
Combine the sweetened condensed milk, sugar, glucose (or corn syrup) and butter in a heavy based saucepan. Stir, without boiling, until the sugar is dissolved.
Bring the mixture to a gentle simmer and simmer while stirring for another 5-6 minutes until the mixture starts to come away from the side of the pan (when you stir, you will clearly see the side or bottom of pan before the mixture covers it up again).
Take the mixture off the heat and mix through the vanilla and white chocolate until fully melted and incorporated.
Set aside while you prepare the top and bottom layers
Melt the milk chocolate in the microwave in 30 second bursts until almost totally melted. Make sure to stir very well between each burst as this will reduce the risk of overheating the chocolate. This should take no longer than two minutes. Stir to finish melting the last few bits.
Add the rice bubbles (rice krispies / puffed rice) into the milk chocolate and stir well. Tip half of the mix into the prepared tin and press it out to the edges with a spatula.
Pour the still warm fudge over the top and tap the tin on the bench top to level it out.
Gently dollop and press the remaining chocolate and rice bubble mix over the top and smooth out.
Leave for 30 minutes to cool at room temperature, then cover with plastic wrap and refrigerate for at least 3 hours or overnight.
Cut into squares and serve.