So, in my experience, there are two types of leaks/explosions when it comes to filled buns. 1. The first is due to the filling not being fully sealed in to the bun. If this is the case, the filling will leak out and pool around the baking buns. You can still salvage these (at least in flavour, if not in presentation), by continuing to bake until the bread rolls are done. Then carefully scoop the exploded filling into a bowl. This will be very hot from the oven. When making your icing, use crumbled filling instead of chopped pistachios to top. 2. The second common issue is if your bread has ended up too thin and the filling expands out the top when baking, causing the bread the break open. You can see in my photos that this happened to one of mine in this bake! This type of leak is a bit less likely to occur on a wide scale, so again just carry on - frost over the exploded bit and the bun will still be perfectly delicious!