Make sure all tools and ingredients are prepared before starting to make each element of the cake. It is easy to forget something once you get going, and there is a fair amount going on in this recipe!
The toffee sauce can be made up to a week in advance. Once made and cool, store in a sealed container in the fridge until ready to use. Warm it up to the right temperature for a drip either in the microwave or by placing the drip bottle in a mug of boiling water.
Be patient when making caramelised white chocolate. If it is heated too quickly, the chocolate will burn and you will need to start over again. You can tell if the chocolate starts burning or seizing up as it will turn grainy and have dark spots. If you notice a grainy patch of chocolate when stirring, no need to panic. Just give it a really thorough mixing to disperse the heat and put it on for less time on next heating, it will all come good! If needed, reduce the microwaving time down to 10 seconds per heating. The whole process does take a while, about a half hour, but it is totally worth the effort!
If you do not have a microwave, you can caramelise chocolate in the oven too. Spread the chocolate on a tray with a lip and heat on a low oven, stirring occasionally, until golden and beautiful. Should you decide to do it in the oven, it will take you a little longer to make, closer to an hour.
Be careful not to spread the caramelised chocolate too thinly for the shards, or you will have very fragile shards for the top of the cake.
Allow the chocolate to set a little before adding the sprinkles so that the sprinkles are not totally sunken into the chocolate.
Set the chocolate until still soft but not completely solid again before marking the shards. Doing this means you will have clean lines for the chocolate to break along, so you can control what each of the shards looks like in shape and size.
When making the buttercream, beating the butter for a good 5 minutes before adding in the sugar will give you a beautiful caramelised white chocolate buttercream to work with. It is extra time and effort, but so worth it, in my opinion!
You can drizzle a little toffee sauce in between the cake layers if want the additional toffee hit. I find the sauce is enough just on top, but if you are a huge toffee fan, there is no reason not to!