Fish Swedish chefs originally served in pastry dishes (6)
I believe the answer is:
pisces
'fish' is the definition.
(I've seen this before)
'swedish chefs originally served in pastry dishes' is the wordplay.
'originally' says to take the initial letters.
'served in' means one lot of letters goes inside another.
'pastry dishes' becomes 'pies' (I've seen this before).
The initial letters of 'swedish chefs' is 'sc'.
'sc' placed into 'pies' is 'PISCES'.
(Other definitions for pisces that I've seen before include "'Sign of the zodiac, the fish (6)'" , "Twelfth sign of the zodiac, the Fish" , "Fish star sign" , "The twelfth sign of the zodiac, the fishes" , "Twelfth zodiacal sign" .)