11yo's Birthday Cake - How to save a cake that's sunk in the middle

I have a confession to make.  I had a major minor baking disaster with my 11yo's Birthday Cake.  I forgot to test it was properly cooked with a skewer when it came out of the oven.  It wasn't quite done and as it started to cool it started to sink in the middle.  I then realised my mistake and put it back in the oven until it was properly cooked but the cake still ended up with a one inch deep dent in the middle.  It looked like a great big chocolate cake crater.  I may have had a mildly hysterical moment at this point.

I didn't have the ingredients, energy or time to make another so had to work with what I had.  I decided to be a bit cunning and use sweets to fill the large crater so nobody would know and I would look like a genius Super Mum for hiding sweets in her cake.  I spread a layer of chocolate ganache, or you could use buttercream over the entire outside of the cake and a thin layer of ganache in the crater to hold the sweets in place.  I then filled the crater with smarties and finished with a layer of chocolate buttons flat side up to provide a flat surface to ice the cake with.  A reasonably thick layer of ganache was carefully spread over the top of the cake, including over the sweets and chocolate buttons.  The cake was then chilled in the fridge overnight so the ganache was really firm which made coating the cake in sugarpaste much easier.

I coated the cake in bright blue sugarpaste and covered it with sugarpaste flowers and buttons, as per my daughters labelled illustration she had given me to work from.  I used this Chocolate Cake recipe to bake the cake.  I baked another Chocolate Cake using that today, made sure I tested it was cooked through after baking, and the cake baked perfectly so I think the sunken cake disaster was a one off, thankfully.