Picnic for Americans with meat served in baked dough (8)
I believe the answer is:
clambake
'picnic for americans' is the definition.
(type of American dish)
'meat served in baked dough' is the wordplay.
'meat' becomes 'lamb' (lamb is a kind of meat).
'served in' means one lot of letters goes inside another.
'baked dough' becomes 'cake' (cakes are made of dough).
'lamb' put into 'cake' is 'CLAMBAKE'.
'with' acts as a link.
(Other definitions for clambake that I've seen before include "Picnic in America" , "Picnic, American style" , "Fishy equivalent of barbecue" , "Outdoor gathering to eat seafood (US)" , "For outdoors" .)