AHi, I have been addicted to this site for a few months now, reading all the posts from you clever people, this is my first post and I do hope someone can help me.

I am making a 3D train cake for my friend's son this weekend, I am doing it in chocolate mudcake with chocolate buttercream covered in fondant, my vanilla buttercream mostly turns out perfect, however, my friend wants chocolate throughout, since I haven't made ganache before I thought I would stick with buttercream but decided to get adventurous and added cocoa AND melted milk chocolate (which I read in CC can be done) and it just became one big lump, I added a bit more milk and that helped a bit and I filled the layers with it but was way too unmaneagable to cover the delicately carved cake with it, I've left the buttercream in the fridge overnight so it's gone really hard, can I save it?? It tastes beautiful but I'm scared to add anything else to it and making it too unstable out of the fridge (since it will have to stay out of the fridge of a couple of days wen the fondant goes on) and also I don't want the fondant to slide off...I did manage to cover the back with it but seemed not to stick to the cake and has now gone into a hard shell on that section so taking it off will be a drama (if I need to make a new batch with a different recipe)

PS I don't have time to make a carve the cake again.

Thanks a million! So excited to read your responses (hope someone does)

AYour buttercream may be too thick. Thin some of it with milk or boiled water for the initial crumb coat. Get it out of the fridge, it needs to be room temp.

AThank you so much for responding I thought I had been forgotten! How long can I leave buttercream out of the fridge without it going bad? If I just whip it a little with a bit more milk (after it goes back to room temp) you think may make it more spreadable? Would adding too much milk make it go bad faster out of the fridge? Sorry about so many questions, any advice would help!

Thanks!

AIt can stay out of the fridge if you use water to thin it. I use hot boiled water, just a tablespoon or so. Butter doesn't need to be refrigerated.

AAnd yes adding more liquid will make it more spreadable.

AThanks so much, you are great help will try that!