Cake mother dear said was filling (7)
I believe the answer is:
madeira
'cake' is the definition.
(I've seen this before)
'mother dear said was filling' is the wordplay.
I cannot really see how this works, but
'mother' could be 'ma' (Ma is another word for mother or mum) and 'ma' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for madeira that I've seen before include "Sponge-cake" , "Atlantic territory" , "Dessert wine from a Portuguese Atlantic island" , "Cake - wine" , "Rich, fortified white wine" .)