Tender tuber regularly used in dish (6)
I believe the answer is:
fondue
'dish' is the definition.
(I know that fondue is a type of dish)
'tender tuber regularly used' is the wordplay.
'tender' becomes 'fond' (synonyms).
'regularly used' indicates alternate letters (letters selected on a regular basis).
The alternate letters of 'tuber' are 'ue'.
'fond'+'ue'='FONDUE'
'in' acts as a link.
(Other definitions for fondue that I've seen before include "Cubes cooked in hot oil and dipped in sauces" , "Dipping sauce" , "Swiss hot cheese dish" , "Melted cheese dip" , "Saucy dish" .)