I tried making some ganache with praline which solidified nicely in the fridge. I was able to shape it into cuboids / bricks and then dip it in tempered chocolate.

But if you look at the photo you can see that after the chocolate had set or started to set the filling started to melt / separate and push its way out of the chocolate like a weed through tarmac. This is really frustrating as I was fairly pleased with the results besides that (the rough and ready look of the chocolates were a bit of a mistake from working at too low a temperature, not one I'll make again).

Do you have any idea why the filling might do that? Does the chocolate contract as it sets, squeezing the filling out? How can I avoid that happening?

This is a little bit of a different direction than I normally take as it has not much to do so much with chocolate making as confection making, but still something many chocolate DIY’ers take on. Something I myself have taken on. So I’ll wade in and give you some of my thoughts and experience. But keep in mind, there may be many other ways to do this and these techniques worked for me. Nearly all of my work here is with truffles.

To answer the most important question, yes, tempered chocolate shrinks when it sets. This is why chocolate pulls away from the mold and releases easily. Unfortunately, this is also what is causing your dipped chocolates to crack and compress the filling out. Since you can’t stop the tempered chocolate from contracting, you have to do something to cope with it pushing your filling out. I have successfully done three different things. All have their plusses and minuses depending on your situation, mindset and the final look you want.

1. Make a ‘hole’ in your filling. It has to be something large enough that you create a small air gap that can compress when the outer covering contracts. A kabob skewer is a little small but will work if you make it a long hole. The working end of a chop stick is good. A thumb is usually too large as the chocolate will just fill in the space.

2. Going off the rift of using a skewer or chop stick, this is often a good way to dip the chocolate also. Just skewer the filling, making sure you are in nice and deep, dip it into your tempered chocolate and then using another chop stick to pull against, remove the stick. In theory, this will leave you with a large enough space inside to collapse and keep your shell intact. The benefit here is cleaner hands. 3. Make a hole in your shell and clean it up. I’ve done this a bit and it works just fine. While you are dipping, just as the outer shell is starting to set up, poke a hole near the bottom (or top if you are doing to decoratively add something to the top). This will control where your filling pushes out and should stop random cracks. Then just go back and dab a touch of chocolate over the hole. Again, if you are putting something decorative on top, or want a little flourish, this is an easy way to take an issue and turn it into a feature.

That’s it. All of those have worked for me. And I will leave you with two things that did not work. Double dipping and trying to cover the cracks. In both cases the new chocolate just shrinks and cracks again.

Oh, and one more. Dip in untempered chocolate and then dust with something. Cocoa powder. Praline powder. Sugar. Something like that. That way your connection does not crack, and the dusting will inhibit and/or prevent the bloom from being seen.

Have fun, and get making those dipped chocolate gifts for the holidays.