Welcome letter contains something tasty (8)
I believe the answer is:
'something tasty' is the definition.
(I've seen this before)
'welcome letter contains' is the wordplay.
'contains' indicates a hidden word.
'OMELETTE' can be found hidden inside 'welcome letter'.
(Other definitions for omelette that I've seen before include "You can't make one without breaking eggs", "Cooked egg dish", "One getting beaten", "Food dish (that can't be made without breaking eggs)", "Beaten-egg dish".)