Any lovely Xmas cake makers ? Advise please !

[Twosugarsplease]

My mil makes Xmas cake every year, sometimes lovely, sometimes not.
Been to visit today and she has made one that has sunk in the middle, otherwise very tasty though. I thought I would ask on here if anyone experienced can give advise on how to prevent this.
She has an electric oven, don't know if that will make a difference.

[LissieLovettsDeliciousPies]

she's opening the door too often or taking it out too early.

[Twosugarsplease]

Ooh, yeah could be a possibility, I'll give her a ring. Thanks for your reply.

[LissieLovettsDeliciousPies]

no problem! good luck. home made cakes are the best. if it looks like its burning on top, pop some foil over!

[Twosugarsplease]

She makes the size of a square biscuit tin lissielovett, so how long in the oven would you recommend ?

[Thumbelina46]

Too much raising agent also causes cakes to sink in middle!I would say about 3 and a half to 4 hrs at about 140 c -sounds like cake is approx.9 inches square(sorry I know I'm not LissieLovett but do have some experience).