Why does a cake sink

[Rouge]

Check the seals on the oven because loose seals can cause cakes to sink too.

I know it sounds silly, but test with a few different cheap packet mixes (like the 99c no brand cake mixes) and see how it goes...

[jaspen]

thanks for the tip rouge - will do - i've been making plenty of vanilla cupcakes with no problem - although they probably aren't as suspect to sinking as this bigger denser chocolate cake or even a big cake in general

[Bathsheba]

Ok Delia emphasises using the correct size tin. She says "the wrong size tin can account for %99 of failed cakes" (presumedly due to sinking). She said that it can be hard to get a good tin these days due to lots of dodgy quality ones out there in non-standard sizes. Apparently they try to undercut each other by making their tins fractionally too small. So maybe check that your tin is the right size for the recipe. I got this info from Delia's white "How To Cook (series one)" book. ETA: most of my tins are from my mother... hand-me-downs that she got over 40 years ago whe she was setting up house. I also buy tins from op Shops... so maybe this means I have standard size tins. The only tin i have bought new was an expensive-at-the-time_but-well-worth-it spring-form tin made in Germany by Kaiser... a standard 20cm round one.