Ruin energy with an almond concoction (8)
I believe the answer is:
marzipan
'almond concoction' is the definition.
(I've seen this before)
'ruin energy with an' is the wordplay.
'ruin' becomes 'mar' (I've seen this before).
'energy' becomes 'zip' (I've seen this in another clue).
'with' says to put letters next to each other.
'mar'+'zip'+'an'='MARZIPAN'
(Other definitions for marzipan that I've seen before include "Cake topping" , "coat often iced over?" , "Cake icing made of ground almonds and sugar" , "Paste on cake" , "Kind of icing, nice on cakes" .)