Fish starters of escargots plated up - all with type of butter (6)
I believe the answer is:
peanut
'all with type of butter' is the definition.
I can't judge whether this definition defines the answer.
'fish starters of escargots plated up' is the wordplay.
'fish' becomes 'tuna' (tuna is a kind of fish**).
'starters of' says to take the initial letters.
'up' says the letters should be written backwards (in down clue: letters go upwards).
The initial letters of 'escargots plated' is 'ep'.
'tuna'+'ep'='tunaep'
'tunaep' backwards is 'PEANUT'.
Can you help me to learn more?
(Other definitions for peanut that I've seen before include "Popular edible seed, often salted" , "Seed also known as a goober" , "Something to eat" , "butter ingredient" , "Dry-roasted or salted snack item" .)