ACan anyone help me please? Whenever I bake a large cake (normally 4 egg mix or over) it collapses in middle about 2/3 of the way through the cooking time?! It's driving me nuts! I tend to level it off after cooking and it still tastes lovely but I can't work out why it keeps doing it? Thank you in advance xxx

Do you mean a cake over 10"?  I always use a heating core for anything over 10"...actually I use a flower nail or two depending on how large it is.  

It is best to use a lower temperature to bake any of your cakes, 325 degrees is great.  Takes a little longer, how much longer depends on your oven and how accurate the temp is.  Also use a metal flower nail or more for cakes over 8".  You can stick one in the center or if I make an 11x15 or 12x18 I use 3 or 4 as needed.  They help conduct the heat to all parts of the cake and make it bake evenly.  HTH.

AThank you ladies I'd never thought of that, I'll give it a go :) xxx

I never use a heating core on any cake - even when I bake a 16" round cake. But I always bake at 325 degrees. Make sure the cake is completely done before removing it from the oven. If a cake isn't 100% baked it will sink in the middle after removed from the oven.

I had the same problem with all my cake batters. I used to bake with both, strips and heating core/nail. 

First I thought it was the pans I use. I have both magic line and wilton, but it wasn't. Then I decided to omit the baking strips and see what happened. problem solved!

For a cake bigger 10"  or larger i use a heating core.
 

AThank you so much for all your posts, I used a metal flower nail and cooked it at 160 and it came out perfect. Thank you so much xxx