I am confused as to why my chocolate mud cake seems to be hollow in the middle when cooked. Any suggestions. This has failed on me a couple of times now. Could it be the seal around the oven?

I'm not sure I understand what you mean by 'hollow'. Did you mean the cake baked and separated leaving an empty spot? Or do you just mean it has large holes in it? It would help if you posted the recipe too.
I know, I'm no help, but I'll try

Hi I had a hole when i did not mix the sugar properly or if you have any thing not mixed correctly. I hope it helps. I had a same problem with my last cake. Try to mix the ingredients at room temperature this might help.

I made a yellow cake once and had the same thing happen.. big holes everywhere.. it was due to improper mixing. I foolishly leftout some flour and just plopped it in at the end without sifting it.. what a disaster.

are you guys talking about big air holes? or something different?

I"ve never made a mud cake but one time I was in a very big hurry and poured batter into a pan - it was quite thick & I poured the batter in so fast it actually formed a large air pocket - result: a huge hollow bubble in the finished cake.

Bang the pans on the counter to "burst the bubbles" in the cake batter.

I'm a banger Debi! Actually dropping it onto my counter 4-5 times get's the air bubbles out! Confuses my husband as to why I am doing it but i like to keep him guessing!

Elle