Dessert product, one taken during exercise (5,3)

'dessert' is the definition.

'product one taken during exercise' is the wordplay.
'product' becomes 'fruit' (fruit can mean the product of something).
'one' becomes 'I' (Roman numeral).
'taken during' means one lot of letters goes inside another.
'exercise' becomes 'pe' (Physical Education).
'i' placed within 'pe' is 'pie'.
'fruit'+'pie'='FRUIT PIE'