Baltic country resort one is at (7)
I believe the answer is:
estonia
'baltic country' is the definition.
(one of the three Baltic nations)
'resort one is at' is the wordplay.
'resort' indicates anagramming the letters.
'one'+'is'+'at'='oneisat'
'oneisat' is an anagram of 'ESTONIA'.
(Other definitions for estonia that I've seen before include "East European country" , "'So eat in here in Tallinn, say (7)'" , "On a site (anag)" , "One of the Baltic States" , "European republic, became independent again in 1991" .)