Small Parisian coat contains old cake (5,4)
I believe the answer is:
petit four
'cake' is the definition.
(petit four is a kind of cake)
'small parisian coat contains old' is the wordplay.
'small parisian' becomes 'petit' ('small' in French).
'coat' becomes 'fur' (fur is a kind of coat).
'contains' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'fur' going around 'o' is 'four'.
'petit'+'four'='PETIT FOUR'
(Other definitions for petit four that I've seen before include "Small fancy cake" , "Delicacy" , "Item of confectionery" , "Bite-sized fancy cake" , "cake or biscuit" .)